Data Analysis of Shipment for Textiles and Apparel from Logistics Warehouse to Store Considering Disposal Risk - MDPI
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sustainability Article Data Analysis of Shipment for Textiles and Apparel from Logistics Warehouse to Store Considering Disposal Risk Rina Tanaka 1 , Aya Ishigaki 1, * , Tomomichi Suzuki 1 , Masato Hamada 2 and Wataru Kawai 2 1 Industrial Administration, Tokyo University of Science, Noda, Chiba 278-8510, Japan; 7418519@ed.tus.ac.jp (R.T.); szk@rs.tus.ac.jp (T.S.) 2 Data-Chef Co., Ltd., Koto-ku, Tokyo 135-0004, Japan; m.hamada@data-chef.co.jp (M.H.); w.kawai@data-chef.co.jp (W.K.) * Correspondence: ishigaki@rs.noda.tus.ac.jp; Tel.: +81-4-7124-1501 Received: 24 November 2018; Accepted: 2 January 2019; Published: 7 January 2019 Abstract: Given the rapid diversification of products in the textile and apparel industry, manufacturers face significant new challenges in production. The life cycle of apparel products has contracted and is now, generally, a several-week season, during which time a majority of products are supposed to be sold. Products that do not sell well may be sold at a price lower than the fixed price, and products that do not sell at all within the sales period may eventually become forced disposal. This creates long-term management and environmental problems. In practice, shipping personnel determine when to ship products to stores after reviewing product sales information. However, they may not schedule or structure these shipments properly because they cannot effectively monitor sales for a large number of products. In this paper, shipment is considered to reduce the risk of product disposal on the premise of selling at a fixed price. Although shipment quantities are determined by various factors, we only consider the change in inventory at the logistics warehouse, since it is difficult to incorporate all factors into the analysis. From cluster analysis, it is found that shipping personnel should recognize a policy to sell products gradually over time. Furthermore, to reduce the risk of disposal, we forecast the inventory from conditional probability and are able to extract products out of a standard grouping using past data. Keywords: apparel products; supply chain management; quick response; clustering; forecasting; sale at fixed price 1. Introduction Environmental problems such as global warming and water shortages along with the expansion of social disparities from globalization not only remain unsolved in the world, they continue to escalate. Thus, the need for companies to play significant roles in shaping sustainable societies is also increasing [1]. A society can be considered sustainable from three perspectives—environmental, societal, and economic [2]; these are often referred to as the triple bottom line or 3BL [3]. Companies must consider the impact of their business activities on the 3BL and establish long-term corporate strategies to minimize adverse impacts in any of these dimensions. By employing this perspective in supply chain management, in particular, companies are more likely to achieve sustainability [4], which in turn can enhance a company’s competitive advantage [5]. Even in the textile and apparel industry—which is subject to the vagaries of fashion and, thus, characterized by short product life cycles—companies are focusing more on sustainability as globalization progresses [6]. In this industry, the emphasis in sustainable supply chain management is placed on effective risk management. Sustainability 2019, 11, 259; doi:10.3390/su11010259 www.mdpi.com/journal/sustainability
Sustainability 2019, 11, 259 2 of 14 In a textile and apparel supply chain, a company’s factories manufacture products according to a designated production plan. Afterwards, via logistics warehouses, the company ships finished products to stores. At the start of a sales period, a quantity of products is made available at stores based on the production plan. At the end of the sales period, it is hoped that inventories of stores and the logistics warehouse will have harmonized with the production plan as well as with customer demand. In practice, however, customer demand often deviates from what is anticipated in the production plan, and a surplus or shortage results. This is because of the long lead times before a sales period [7] and because apparel products are seasonal, that is, usually only one season. Further, in the textile and apparel industry, the logistics warehouses serve as stock points, and therefore, decisions about shipments to logistics warehouses are crucial [8]. In recent years, as customer needs and preferences have proliferated, textile and apparel products have been made available in an ever-widening range of colors and sizes [9]. Moreover, an increasing number of manufacturers also sell more general apparel products—such as bags, shoes, and accessories—in addition to clothes [10]. Because of these trends, leading to modifications in the design of apparel products every season, demand uncertainty in the industry is large compared to that for industries with more stable products, such as office supplies, or furniture. In other words, every season there are new apparel products with very short life cycles [9]. Therefore, it is difficult to forecast when and which products will be sold at any given time [11]. Many factors are at play in textile and apparel supply chains. When shipping products from the production plants to the logistics warehouse, timing and quantities are determined in advance. On the other hand, when shipping from the logistics warehouse to stores, timing and quantities can be modified in accordance with customer demand by taking into account actual sales information. The earlier that shipments are sent from the logistics warehouse, the higher is the possibility that inventory at the stores will become excessive, such that unsold products will eventually be returned to the logistics warehouse and discarded. Inventory space in a store may also be quite limited, resulting in the need to return or dispose of excess product. In contrast, when shipments from the logistics warehouse are delayed, stores can experience shortages and, as a result, lose opportunities for sales. In addition, because of long lead times before sales seasons, trends may have already have shifted by the time the season arrives, with the result that product designs will have become unsuitable for selling. Shipping personnel are responsible for controlling inventory by determining shipments (timing and quantities) from the logistics warehouse to stores. Normally, these personnel rely on signals from stores when deciding if additional shipments are necessary [12]. Because of the range of products and frequency of shipments, however, it is difficult for them to efficiently and accurately track all sales information. These shortcomings can result in excess product, the proper disposal of which has become a significant environmental problem. The textile and apparel industry is the second largest industry in the world; as such, it can have an enormous impact on the global environment [13], particularly since waste is generated at every stage of in the apparel manufacturing process [14]. In sum, the disposal of excess product within the apparel industry is an increasing threat to the environment [15]. To minimize the quantity of unsold product, manufacturers should more carefully consider customer demand when making production decisions. In this way, they can fulfill their role in helping to build a sustainable society, at least from an environmental perspective. From an economic perspective, manufacturers face another related challenge: anticipating a disposal problem, they may significantly lower the price of products to try to sell more product and, hence, mitigate the challenge of disposal. An increase in the number of unsold products at the end of a sales cycle, then, would lead to an increase in the number of products whose price was discounted by the company. If this cycle were to continue, profits would inevitably decline and sustaining the business over the long term would become more difficult. To prevent problems such as this in the economic dimension, companies would need to increase or at least maintain the number of products sold at a fixed price.
Sustainability 2019, 11, 259 3 of 14 On the premise of selling at a fixed price, we consider the timing of shipping as a method to reduce waste risk due to unsold inventory in this study. Initially, the sales scenario of the products that the shipping personnel need to monitor is restricted. Next, in consideration of the need to sell these products at a fixed price, personnel forecast the inventory ratio in the sales period and consider shipping timing in order to reduce the disposal risk. 2. Literature Review Unsustainable and unregulated production and consumption are contributing to the degradation of the global environment [16]. Proper monitoring and analysis in the textile and apparel supply chain is necessary to minimize its environmental impact [17]. A literature review on the apparel supply chain is as follows. The sustainability of the textile and apparel supply chain has two aspects: environment sustainability such as reduction of unsold products and economic sustainability that improves return on investment (ROI) [18]. With environment sustainability, manufacturers are required to manage resource procurement, inventory, waste treatment, and transport efficiently. On the other hand, with economic sustainability, manufacturers are required to increase the number of products sold at regular price and have large sales. Caniato et al. investigated large and small companies on the problem of environment sustainability in fashion supply chain [19]. As a result, large companies tend to focus more on improving products and processes, and small and medium companies tend to rebuild supply chains. Choi and Chiu proposed the mean-downside-risk (MDR) and mean-variance (MV) newsvendor model considering both environment sustainability and economic sustainability [20]. Brun and Castelli explored specific factors or product characteristics that promote competition in the fashion industry [21]. Čiarnienė and Vienažindienė identified key features of the modern fashion industry and developed a time efficient supply chain model [22]. Mehrjoo and Pasek described the structure of the apparel supply chain using system dynamics and quantitatively evaluated its risk [23]. Patil et al. developed a mathematical model to evaluate procurement, shipping, and markdown plans for new short-term life cycle products considering discounts associated with large-scale purchase and bulk transport [24]. In order for the shipping personnel to recognize when to send additional shipments, they rely on signals that indicate when products have been sold at stores. This system is known as Quick Response (QR), and it has demand-driven characteristics. Quick Response reduces lead time and allows shippers to quickly respond to market needs [25]. It was first implemented in the US apparel industry in the middle 1980s as a strategy for global response [26] and, since then, its use has spread to other industries. It was designed to be an inventory management strategy that was based on sharing information among supply chain agents [27]. By using a QR strategy, lead time is shorter because the shipping personnel can better forecast customer demand and subsequently modify the production plan [25]. In basic QR, a retailer sends point of sale (POS) data to its supplier, who then uses this information to improve demand forecasting [28]. Tsukagoshi et al. proposed using a QR inventory management strategy of introducing a monitoring period prior to the normal sales period in cases for which replenishment lead time is short compared to the sales period. They found that this approach reduced total shortage costs [29]. Tanaka et al. analyzed shipping data on the premise of selling at a fixed price [8]. They considered the risk of running out of stock but not the risk of disposal of unsold products. In the apparel market, sales forecasting plays an increasingly important role in decision support systems for market competition and globalization [30]. Thomassey explained specific constraints and needs related to supply chain and sales forecasts in the textile apparel industry [31]. In a large set of SKUs and two consecutive sales seasons, Mostard et al. compared the accuracy of three quantitative forecasting methods based on advance demand information [11]. Fan et al. proposed a prediction model combining the Bass/Norton model and the sentiment analysis method [32].
Sustainability 2019, 11, 259 4 of 14 Sustainability 2019, 11 FOR PEER REVIEW 4 3. Status of Products 3. Status In general, of Products a manufacturer stores new products in one logistics warehouse for each supply chain. Sustainability 2019, 11 FOR PEER REVIEW 4 Also, a range of products In general, can bestores a manufacturer shippednewfrom oneinlogistics products warehouse one logistics warehouse tofor multiple stores, each supply but the chain. 3. 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For this reason, we analyze the specific from of shipping products oneand quantities logistics shipped depend warehouse on the unique to one store. Hence,properties of stores, in this paper, the such as clientele, textile and apparel composition of shipping from one logistics warehouse to one store. Hence, in this paper, the textile supply sales floorisspace, chain and geographic considered as shown location in theorFigure climate.1.IfThis one attempts supply to consider chain all themultiple includes characteristics factories, and apparel supply chain is considered as shown in the Figure 1. This supply chain includes multiple of storeswarehouse, one logistics in detail, the onescope store,ofand the many data becomes customers. veryProducts large. Forarrive this reason, in the we analyze logistics the warehouse factories, one logistics warehouse, one store, and many customers. Products arrive in the logistics composition of shipping from one logistics warehouse to one store. Hence, in this paper, the textile from warehouse multiple factories, and then from multiple the shipping factories, and then personnel the shipping ship products personnel that ship have arrived products that havein arrived the logistics and apparel supply chain is considered as shown in the Figure 1. This supply chain includes multiple warehouse to one store. in the logistics warehouse to one store. factories, one logistics warehouse, one store, and many customers. Products arrive in the logistics warehouse from multiple factories, and then the shipping personnel ship products that have arrived in the logistics warehouse to one store. Figure 1. 1.Conceptual Figure Conceptual Diagram ofSupply Diagram of SupplyChain Chain Flow. Flow. Then, we consider Then, we consider inventory inventorychange changein in our our logistics warehouse. logistics warehouse. Figure Figure 2 shows 2 shows changes changes in thein the Figure 1. Conceptual Diagram of Supply Chain Flow. percentages percentages of the inventories of the inventories ofofproducts products in in an an actual logisticswarehouse. actual logistics warehouse. As shown As shown in Figure in Figure 2, 2, there are there are products products with inventory with inventory ratios ratios of zero of zero in the logistics inlogistics the logistics warehouse warehouse at nine weeks, while some Then, we consider inventory change in our warehouse. Figureat nine weeks, 2 shows changes while in thesome products products remain remainin in high high proportions.Figure proportions. Figure33 shows shows aahistogram histogram ofofthetheinventory inventory ratios at the ratios at ninth the2,ninth percentages of the inventories of products in an actual logistics warehouse. As shown in Figure week. week.there Theare The ratio ratio is less is lesswith than than 0.10 for most 0.10 forratios products, mostofproducts, but there are still products with considerable products inventory zero in the but there logistics are still products warehouse at nine weeks,with considerable while some inventory remaining. There are two reasons why large inventories for a product could persist. The products inventory remain in high remaining. There proportions. Figure 3 shows are two reasons why largea histogram of the inventory inventories ratios atcould for a product the ninthpersist. first is overproduction, that is, a discrepancy between scheduled and actual sales of product. As a week. The first is The ratio is less than overproduction, 0.10 that is,for most products, a discrepancy but there between are still products scheduled and actual with sales considerable of product. countermeasure, there is the method of discounting and selling inventory or selling it through inventory remaining. As a another countermeasure, There there are method two reasons why large inventories for inventory a product could persist. through The channel, such asisanthe of discounting electronic commerce and selling (EC) site. The second or selling potential cause isit that first is overproduction, that is, a discrepancy between scheduled and actual sales of product. As a another channel, shipments such have as an been electronic timed poorly.commerce The shipping (EC) site. Theare personnel second the onespotential cause is that who determine shipments the timing countermeasure, there is the method of discounting and selling inventory or selling it through have and beenquantities timed poorly. The shipping personnel are the ones who determine of products to be shipped based on sales information. However, due to the challenge the timing and quantities another channel, such as an electronic commerce (EC) site. The second potential cause is that of products of managing to beashipped large numberbasedofon sales information. products, personnel may However, overlook adue signal shipments have been timed poorly. The shipping personnel are the ones who determine the timing to the thatchallenge a product has of managing sold at a largeits fixed price. number of If the number products, of unsold personnel may fixed-price overlook products a signal increases, that a there has product and quantities of products to be shipped based on sales information. However, due to the challenge will sold be anatincrease its fixed inprice. If theinventory number of managing in unsold of need of fixed-price disposal at the a large number of products, end of the products sales period. increases, personnel may there After will be overlook considering an increase a signal sustainability, in inventory that a product firms has soldinatneed should of disposal increase atprice. the end the number of the of products salesofperiod. sold at a fixed price as much as possible. its fixed If the number unsold After considering fixed-price productssustainability, increases, therefirms should will be increase an increase in the inventory 1.00 in need of disposal at price the end number of products sold at a fixed as of the sales much period. After considering sustainability, firms as possible. 0.90 the number of products sold at a fixed price as much as possible. should increase 0.80 1.00 Ratio Ratio 0.70 0.90 0.60 0.80 Inventory 0.50 0.70 Product 1 0.40 0.60 Product 2 Inventory 0.30 0.50 Product 1 Product 3 0.20 0.40 Product 2 0.10 0.30 0.00 Product 3 0.20 0.10 0 1 2 3 4 5 6 7 8 9 0.00 Week 0 1 2 Figure 2.3 Example 4 of Inventory 5 6 Ratio 7 Change. 8 9 Week Figure Figure 2. 2. Exampleof Example ofInventory Inventory Ratio RatioChange. Change.
Sustainability 2019, 11, 259 5 of 14 Sustainability 2019, 11 FOR PEER REVIEW 5 500 450 400 350 300 Frequency 250 200 150 100 50 0 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 Inventory Ratio Figure3.3.Histogram Figure Histogramof ofInventory InventoryRatio Ratioin inNinth NinthWeek. Week. 4. Methods 4. Methods In this paper, we assume the supply chain as shown in the Figure 1. Since the sales cycle of the In this paper, we assume the supply chain as shown in the Figure 1. Since the sales cycle of the textile and apparel supply chain is one week [33], we perform our analysis using weekly data. The data textile and apparel supply chain is one week [33], we perform our analysis using weekly data. The used in this paper is collected in the logistics warehouse. data used in this paper is collected in the logistics warehouse. 4.1. Assumptions, Parameters, and Variables 4.1. Assumptions, Parameters, and Variables In this paper, the following assumptions, parameters, and variables are used. The parameters and In this variables are paper, the in described following subsequent assumptions, sections. parameters, and variables are used. The parameters and variables are described in subsequent sections. Assumptions: Assumptions: • Products are sold in the same period • Products are sold in the same period • The total arrival quantity of each product is known • The total arrival quantity of each product is known • Product movement among stores is not considered • Product movement among stores is not considered •• The Theperiod periodininwhich whichproducts productsare aresold soldatatthe thefixed fixedprice priceisisnine nineweeks weeks •• Since Since products are sold up for nine weeks, the sales period isnine products are sold up for nine weeks, the sales period is nineweeks weeks •• IfIfthe product did not sell for nine weeks, the product is discarded the product did not sell for nine weeks, the product is discarded Parameters and Variables: Parameters and Variables: N: number of products N: number of products T: sales period [weeks] T: sales period [weeks] t: elapsed periods [weeks] (t = 1, …, T) t: elapsed i: productperiods [weeks] number (i =(t1,= …, . . , T) 1, . N) i: product di (t): number shipping(iamount N)product i in week t = 1, . . . ,of di (t): Dshipping amountamount i: total delivery of product i in week of product i t Di : total delivery amount of product ui (t): shipping rate in week t of product i i ui (t): K: numberrate shipping of clusters in week t of product i K: number of clusters sales period T’: investigated I i ,t : inventory T’: investigated salesratio periodof product i in week t Ii,t : inventory X i : random ratio of product i in week t variable representing the realized inventory ratio of product i Xi : random variable representing the realized inventory ratio of product i Yi : random Yi : random variable representing the predicted inventory ratio of product i variable representing the predicted inventory ratio of product i μ ′ : conditional µ0 : conditional expectation expectation
Sustainability 2019, 11 FOR PEER REVIEW 6 Sustainability 2019, 11, 259 6 of 14 μX : average of X i μY : average µ X : average of Xi Y of i µY : average of Yi ρ: correlation coefficient ρ: correlation coefficient σ x : variance of X i σx : variance of Xi σ Y : variance σY : variance of Yi of i Y 0 σ : variance in conditional probability σ ′ : variance in conditional probability 4.2. Decision-Making Process for Shipping Personnel 4.2. Decision-Making Process for Shipping Personnel Based on the above parameters and variables, Figure 4 shows the decision-making process Based on the above parameters and variables, Figure 4 shows the decision-making process of of shipping personnel. It has seven steps. This paper proposes methods for supporting shipping shipping personnel. It has seven steps. This paper proposes methods for supporting shipping personnel who are in charge of each decision-making process. personnel who are in charge of each decision-making process. Figure 4. Decision-Making Process for Shipping Personnel. Figure 4. Decision-Making Process for Shipping Personnel. These steps are for product i. These steps are for product i. Step 1. Product i arrives at the logistics warehouse from a plant, and its quantity is Di . Step 1. Product i arrives at the logistics warehouse from a plant, and its quantity is Di. Step Step2.2. Shipping personnel Shipping practice personnel firstfirst practice shipment shipmentof product i based of product on a sales i based on apolicy which is sales policy givenis which by given manufactures and its quantity is by manufactures and its quantity d i (1). is di (1). Step 3. Shipping personnel recognize sales information Step 3. Shipping personnel recognize sales information of product of producti fori for oneone week. week. Step 4. Shipping personnel consider and decide whether to ship additional Step 4. Shipping personnel consider and decide whether to ship additional product product during during the next the next week. At this time, they refer not only to sales quantity of product i but also week. At this time, they refer not only to sales quantity of product i but also to sales to sales information of similar products information sold last of similar year and products soldcurrent trends. last year and current trends. Step Step5.5. Based Basedon on shipping personnel shipping personnel decision, decision,product i is shipped product whose i is shipped quantity whose is di (t) quantity is dat t-th i (t) at t-th week. week.In the determination In the determination of the of quantity, the quantity,the inventory the inventory of theofstore the and storethe and scale theof the store scale of the arestore takenareintotaken into consideration. consideration. Then, if decide Then, if personnel personnel not decide to makenot to make anshipment, an additional additional shipment, shipping shipping quantity of the productofdithe quantity (t) product is zero. di (t) is zero. Step6.6. If the Step If the next next week, week, t + t1,+ is 1, end is end of sales of sales period period T, go T, go to Step to Step 7. Otherwise, 7. Otherwise, shipping shipping personnel personnel return return to Step to Step 3 and 3 and repeat repeat fromfrom StepStep 3 to3 Step to Step 5 until 5 until they they fulfill fulfill StepStep 6. 6. Step7.7. Shipping Step Shipping personnel personnel finish finish their their decision. decision.
Sustainability 2019, 11, 259 7 of 14 4.3. Product Data Extraction Products in the apparel and textile industry come in many categories, colors, and sizes; thus, Sustainability the amount of 2019, 11 FOR product available PEER REVIEW data enormous. Further, customer demand is uncertain, and7sales area affected by fashion and other industry trends that are in a state of constant flux. In light of these 4.3. Product Data Extraction circumstances, the data that shipping personnel have access to at any given time is limited in scope. Therefore,Products in the apparel when analyzing ourand owntextile data,industry we dividecome thein many categories, products colors, and into several sizes; thus, groups, the data extract amount of available product data enormous. Further, customer demand is uncertain, and sales area from products likely to require shipping plan revision, and analyze them. affected by fashion and other industry trends that are in a state of constant flux. In light of these An example of the actual change in inventory in a logistics warehouse is shown in Table 1. There is circumstances, the data that shipping personnel have access to at any given time is limited in scope. a significant Therefore, difference in product when analyzing our quantities own data, we even in the divide the first week, into products making it difficult several groups, to see inventory extract data transitions of all products from products likely toon one scale require of inventory shipping quantity. plan revision, Therefore, and analyze them.the shipping ratio is calculated as the incoming An example inventory in each of the actual week change di (t), normalized in inventory in a logisticsbywarehouse the total isarrival in Table 1.D shown quantity i of each There is ai:significant difference in product quantities even in the first week, making it difficult to see product inventory transitions of all products on one scale ofdinventory (t) quantity. Therefore, the shipping ratio ui ( t ) = i . (1) is calculated as the incoming inventory in each weekD dii(t), normalized by the total arrival quantity Di of each product i: After calculating the shipping rate for each product, a k-means cluster analysis of ui (t) is conducted for t = 1, . . . , 9, with a sample of N = 796 uin(order dito( t divide ) i t) = . products into groups. Since the (1) number of pieces of data is as large as N = 796, we decided Di to use nonhierarchical instead of hierarchical clustering.After calculating To calculate thethe shipping distance rate forsamples, between each product, a k-means Euclidean cluster distance analysis is used. One of ui(t) is disadvantage of the k-means method is the dependence on the initial value. Therefore, some initial valuesthe conducted for t = 1, …, 9, with a sample of N = 796 in order to divide products into groups. Since are set numberanalysis and cluster of piecesis of data is as and performed, largeinitial as N values = 796, we are decided chosen toto minimize use nonhierarchical instead the distance withinof the hierarchical clustering. To calculate the distance between samples, Euclidean distance is used. One average cluster. The results of the cluster analysis leads to patterns, here called sales policies (i.e., disadvantage of the k-means method is the dependence on the initial value. Therefore, some initial policies involving selling by advertising products that will be recognized by customers vs. policies to values are set and cluster analysis is performed, and initial values are chosen to minimize the distance sell normally, within theasaverage standard products). cluster. The results of the cluster analysis leads to patterns, here called sales policies (i.e., policies involving selling by advertising products that will be recognized by customers Table 1. Examples of Changes in Inventory. vs. policies to sell normally, as standard products). Change in Inventory in Each Week Table 1. Examples of Changes in Inventory. Product 0 2 1 3 4 5 6 7 8 9 Change in Inventory in Each Week A 2884 291 266 240 198 154 123 80 44 36 Product 0 1 2 3 4 5 6 7 8 9 B 2078 1151 1038 347 221 171 122 0 0 0 AC 2884293 291 249 266248 240 220 198 220 154 220 123 191 11680 94 44 32 36 B 2078 1151 1038 347 221 171 122 0 0 0 C 293 249 248 220 220 220 191 116 94 32 The result of the k-means method suggested that it was reasonable to divide the analyzed data into two groups, which The result of thewere k-meansthen roughly method dividedthat suggested into five reasonable it was groups to toprovide divide more detail. data the analyzed Figure 5 shows into thetwo groups, average which value ofwere then roughly inventory ratios divided in each into week fiveforgroups to the each of provide five more detail. clusters. Figure 5 on Depending shows thepercentages the shipment average valueinofthe inventory ratios first week, in each five weekcan clusters forbeeach of the five broadly clusters. Depending on categorized. the shipment percentages in the first week, five clusters can be broadly categorized. 1 0.9 0.8 0.7 Inventory Ratio 0.6 0.5 0.4 0.3 0.2 0.1 0 0 1 2 3 4 5 6 7 8 9 Week 1 2 3 4 5 Figure 5. Average Figure 5. AverageInventory InventoryRatios in Each Ratios in EachWeek Weekfor forEach Each Cluster. Cluster.
Sustainability 2019, 11, 259 8 of 14 For clusters 1 and 2, the shipment ratio in the first week is high. On the other hand, in clusters 3, 4, and 5, the shipment ratio of the first week is low. Investigating the characteristics of each cluster further, products of clusters 1 and 2 represent the policy that a manufacturer wants to sell featured products. Also, the trend of shipment ratios from the second to the ninth week shows that products remaining in the logistics warehouse are gradually shipped until the end of the sale period. Therefore, the shipping personnel will not revise the shipping plan later. On the contrary, products in clusters 3, 4, and 5 demonstrate a policy whereby the shipping personnel sell the product in stages, conditional on the level of sales. Accordingly, products belonging to these classes are highly likely to have been subject to revised shipping plans. In other words, shipping personnel should have recognized products exhibiting this kind of sales information. 4.4. Forecasting Inventory Ratios The cluster analysis identifies products that shipping personnel should recognize as undergoing significant changes in inventory. However, the shipping personnel do not know the optimal time or other factors about the shipment. Therefore, the reference lines obtained by cluster analysis (Figure 5) predict the inventory ratio at certain weeks. Changes in inventory that deviate significantly from the basic line are signals that should be transmitted to shipping personnel to highlight important sales information. In this paper, to predict how far the inventory transition will be from the basic line, the conditional probability of the bivariate normal distribution is used for each product. In this way, it is possible to predict the subsequent inventory transition when the change in inventory is recognized until a specific week. The conditional expectation and variance in the conditional probability of the bivariate normal distribution are obtained by the following Equations (2) and (3), respectively. Ii,t − µ X µ0 = µY + ρσY , (2) σx q σ0 = σY 1 − ρ2 (≤ σY ). (3) Based on the above conditional expectation and the conditional variance of the conditional probability, a 95% confidence interval is generated, which is used as the range of prediction. However, since the actual inventory ratio may be smaller than the inventory ratio considering 95% confidence intervals for the conditional expectation obtained by the conditional probability of the bivariate normal distribution, this paper proposes minimum values for each week. Since the inventory ratio cannot be smaller than zero, it is considered to be the minimum. Hence, the upper and lower limits of the range from the inventory ratio considering the 95% confidence interval and the actual inventory ratio are as follows: Upper limit : Min µ0 + 1.96σ0 , Ii,t , (4) Lower limit : Max µ − 1.96σ0 , 0 . 0 (5) Here, we predict the inventory ratio of product A using information on all clusters of products to be sold in stages, namely, clusters 3, 4, and 5, and for the cluster to which it belongs, 3. The prediction for product A is shown below. The gray line of each figure is a line connecting the conditional expectation values at each week calculated by the Equation (2). The blue line represents change of the upper limit value in each week obtained from Equation (4). The orange line shows change of the lower limit derived from Equation (5). Finally, in order to compare how the actual inventory ratio changes to changes of gray, blue, orange lines, the change of the actual inventory ratio is indicated by yellow line. Here, the calculation results are shown assuming that the sales period is T = 9. Therefore, based on the assumption, the products will not be sold after nine weeks and will be discarded.
Sustainability 2019, 11, 259 9 of 14 Sustainability 2019, 11 FOR PEER REVIEW 9 The shipment The shipment of of the the first first week week isis determined determined by by the the manufacturer’s manufacturer’s sales sales policy, policy, and and shippers shippers who oversee shipping decisions begin shipping after the second week. Therefore, who oversee shipping decisions begin shipping after the second week. Therefore, this paper predicts this paper predicts inventory levels inventory levels for forall allweeks, weeks,conditional conditional onon thethe realized level realized of sales level up toup of sales anytogiven week. week. any given Form Figure 6a,b, since the shipping ratio at the third week is large, the range of prediction Form Figure 6a,b, since the shipping ratio at the third week is large, the range of prediction after the after the fourth week can fourth weekbecan narrowed be narrowedsignificantly. significantly.Furthermore, Furthermore,with thethe with expected expectedvalue valueof of the conditional the conditional probability, which probability, which isis the the gray gray line, line, at at the the time time when when thethe inventory inventory ratio ratio up up to to the the second second week week isis known, the inventory ratio of the ninth week has already come close to the actual known, the inventory ratio of the ninth week has already come close to the actual inventory ratio. inventory ratio. Therefore,in Therefore, inthe thecase caseofofproduct productA, A,the theinventory inventoryratio ratiothat thatwill will result result inin disposal disposal could could bebe predicted predicted at at the the second second week.week. Shipping Shipping personnel personnel who know who know this this can canreduce then then reduce the amount the amount of product of disposal product disposal by by considering considering various countermeasures various countermeasures and takingand taking action. action. 1 1 0.8 0.8 Inventory Ratio Inventory Ratio 0.6 0.6 0.4 0.4 0.2 0.2 0 0 0 2 4 6 8 0 2 4 6 8 Week Week (a) (b) 1 1 0.8 0.8 Inventory Ratio Inventory Ratio 0.6 0.6 0.4 0.4 0.2 0.2 0 0 0 2 4 6 8 0 2 4 6 8 Week Week (c) (d) Figure 6. The Figure 6. The Expectation Expectation for Product Product A A (conditional (conditional on data of clusters clusters 3, 4,4, and and 5). 5). Note: Note: graph (a) represents representswhen whenthe theactual actualinventory inventoryratio ratiois is known known byby thethe second secondweek, (b)(b) week, is when it isitknown is when is knownby the by third week, (c) is when it is known by the fourth week, and (d) is when it is known the third week, (c) is when it is known by the fourth week, and (d) is when it is known by the fifth by the fifth week. The gray week. Theline grayshows the conditional line shows expectation, the conditional the blue expectation, theand orange blue lines show and orange linesthe showupper and lower the upper and limits lower of the range, limits of the respectively, and theand range, respectively, yellow the line shows yellow linethe change shows the in the actual change in theinventory ratio of actual inventory product A. ratio of product A. In both Figures 6 and 7, the more weeks in which the inventory ratio is known, the narrower the In both Figures 6 and 7, the more weeks in which the inventory ratio is known, the narrower range of prediction. In the case of product A, the prediction range is narrowed significantly in the the range of prediction. In the case of product A, the prediction range is narrowed significantly third week. This is because the actual inventory ratio of product A is drastically reduced in the third in the third week. This is because the actual inventory ratio of product A is drastically reduced week. Moreover, in the third week.when predicting Moreover, whenwith only the predicting cluster with to which only the clusterproduct to which A product belongs,Athe prediction belongs, range the prediction range is narrowed as a whole. However, product A is shipped at a high rate inThen, is narrowed as a whole. However, product A is shipped at a high rate in the third week. the the inventory third week. ratio at the Then, thethird week ratio inventory is much smaller at the third than weekthe expected is much inventory smaller ratio than the of the third expected week at the inventory second ratio week. of the third The weekactual at thesales areweek. second not known at that The actual time, sales are but not shipping known at more than the that time, expected but shipping more than the expected value may result in more waste. Hence, excess shipping the value may result in more waste. Hence, excess shipping can be reduced by shipping product in the fourth can be reduced week after by shipping the receiving product in more the detailed fourth weeksalesafter information. receivingInmoreotherdetailed words, sales since this product is highly information. likelywords, In other to result in some since this disposal, product isit is possible highly to reduce likely extra to result shipping in some by lengthening disposal, it is possible to reduce extra shipping by lengthening the period for recognizing sales information.
Sustainability 2019, 11, 259 10 of 14 Sustainability 2019, 11 FOR PEER REVIEW 10 As the in the other period method, when for recognizing salesshipping at theAs information. third week, in the it method, other is better when to adjust the shipping shipping at the third amount week, it of product is better to A. For the adjust example, product shipping A isofshipped amount productatA.proportions For example,according producttoAthe basic at is shipped line (gray line proportions of Figureto6 the according or Figure 7). (gray line of Figure 6 or Figure 7). basic line 1 1 0.8 0.8 Inventory Ratio Inventory Ratio 0.6 0.6 0.4 0.4 0.2 0.2 0 0 0 2 4 6 8 0 2 4 6 8 Week Week (a) (b) 1 1 0.8 0.8 Inventory Ratio Inventory Ratio 0.6 0.6 0.4 0.4 0.2 0.2 0 0 0 2 4 6 8 0 2 4 6 8 Week Week (c) (d) TheConditional Figure 7. The ConditionalProbability ProbabilityExpectation Expectationofofthe theBivariate Bivariate Normal Normal Distribution Distribution of of Product Product A A for Data of Cluster 3. Note: graph (a) represents when the actual inventory for Data of Cluster 3. Note: graph (a) represents when the actual inventory ratio is known by ratio is known by the second week, second week, (b) (b) is is when when itit is is known known by by the the third third week, week, (c)(c) is is when when itit is is known known byby the the fourth fourth week, week, when it is and (d) is when is known known by by the the 5th 5th week. week. The The gray gray line line shows shows thethe conditional conditional expectation, expectation, the blue and orange lines show the the upper upper and and lower lower limits limits of of the therange, range,respectively, respectively, and the yellow line shows shows the change in the actual inventory ratio of product A. As aa second As second example, example, thethe prediction prediction results results for for product product B B are are shown shown in in Figures Figures 88 and and 9. 9. Product Product B is also sold in stages, and the detailed cluster number is 5. As with product B is also sold in stages, and the detailed cluster number is 5. As with product A, we predict cases A, we predict cases for which the actual inventory ratio is known in the second week. The figures show that product B has B for which the actual inventory ratio is known in the second week. The figures show that product a has ainventory high high inventory ratioateven ratio even at theweek. the ninth ninth Also, week.inAlso, in the the case of case productof product B, the predicted B, the predicted ninth ninth week’s week’s inventory inventory ratio atratio the at the second second weekweek does does not differ not differ much muchfrom fromthethe prediction prediction atatthe thefifth fifthweek. week. Therefore, some degree of prediction is possible in the second week. Furthermore, Therefore, some degree of prediction is possible in the second week. Furthermore, as can be seen as can be seen in in Figure 9d, the inventory ratio at the sixth week is lower than the expected Figure 9d, the inventory ratio at the sixth week is lower than the expected value, suggesting that value, suggesting that shipments were shipments were made made to to avoid avoid being being left left with with aa large large inventory inventory in in the thelogistics logisticswarehouse. warehouse.However, However, since the product is unlikely to sell much after being shipped in the since the product is unlikely to sell much after being shipped in the sixth week, perhaps it sixth week, perhaps it should should have been shipped earlier to increase sales. By shipping in this manner, the product have been shipped earlier to increase sales. By shipping in this manner, the product would have been would have been placed in placed in the the store store for for aa longer longer period, and opportunities period, and opportunities to to sell sell atat the the fixed fixed price price would would alsoalso have have increased. This would have reduced the amount of waste due increased. This would have reduced the amount of waste due to unsold product. to unsold product. When using the results of prediction, first, the shipping personnel would compare the conditional expectation with the inventory ratio of the product at the present moment. This shows how the inventory ratio of the product changes with respect to the average. Then, the shipping personnel would plan the shipping for the next week. Finally, they would determine the amounts of the shipment while also taking into account the sales policy.
Sustainability 2019, 11, 259 11 of 14 Sustainability 2019, 11 FOR PEER REVIEW 11 1 1 0.8 0.8 Inventory Ratio Inventory Ratio 0.6 0.6 0.4 0.4 0.2 0.2 0 0 0 2 4 6 8 0 2 4 6 8 Week Week (a) (b) 1 1 0.8 0.8 Inventory Ratio Inventory Ratio 0.6 0.6 0.4 0.4 0.2 0.2 0 0 0 2 4 6 8 0 2 4 6 8 Week Week (c) (d) Figure 8. TheFigure 8. The Expectation Expectation of Product of Product B (conditional on B (conditional ondata dataforfor clusters 3, 4, and clusters 5).and 3, 4, Note:5). graph (a) graph (a) Note: represents when the actual inventory ratio is known by the second week, (b) is when it is known by represents when the actual inventory ratio is known by the second week, (b) is when it is known by the the third week, (c) is when it is known by the fourth week, and (d) is when it is known by the fifth third week, (c) is week. Thewhen it isshows gray line known by the fourth the conditional week,the expectation, and blue(d) andisorange whenlinesit isshow known by the the upper andfifth week. The gray linelower shows the limits of theconditional expectation, range, respectively, the blue and the yellow line and shows orange lines the change in show theinventory the actual upper and lower limits of theratio of product range, B. respectively, and the yellow line shows the change in the actual inventory ratio of Sustainability 2019, 11 FOR PEER REVIEW 12 product B. Also, the results of this prediction lead to different recommendations depending on the type of product. 1 For example, in the case of a standard product, 1 manufacturers sell for a longer term, so if the inventory runs out earlier than forecasted, it is possible to produce additional products to meet 0.8 0.8 customer demand. On the other hand, in the case of a product sold for only one season, when the Inventory Ratio Inventory Ratio expected 0.6 value of the stock ratio at the ninth week is large, 0.6 this is a signal that products are not selling well that should be heeded by shipping personnel. 0.4 0.4 In QR strategy in the logistics warehouse, product shipping quantities are decided at the time when0.2shipping personnel receive sales information on 0.2each product during the monitoring period. However, in this paper, we give a signal to shipping personnel that is based on the comparison of previous 0 inventory transition for a similar product to the 0 current inventory transition for the current 0 2 4 6 8 product.0 Therefore, 2 even 4if there is 6 8 no arrival of sales information, shipping personnel can receive Week Week signals about shipping. In addition, this method is effective for all sales periods. (a) (b) 1 1 0.8 0.8 Inventory Ratio Inventory Ratio 0.6 0.6 0.4 0.4 0.2 0.2 0 0 0 2 4 6 8 0 2 4 6 8 Week Week (c) (d) Figure 9. Figure 9. The Conditional The Conditional ProbabilityExpectation Probability Expectation of of thethe Bivariate NormalNormal Bivariate Distribution of Product Aof Product Distribution for Data of Cluster 5. Note: graph (a) represents when the actual inventory ratio is known by the A for Data of Cluster 5. Note: graph (a) represents when the actual inventory ratio is known by the second week, (b) is when it is known by the third week, (c) is when it is known by the fourth week, second week, (b) and (d) is is when when it is it is known known by the by fifththe third week. The week, gray line(c)shows is when it is known the conditional by the the expectation, fourth week, and (d) is blue whenanditorange is known by the lines show thefifth week. upper Thelimits and lower grayofline the shows the conditional range, respectively, and theexpectation, yellow line the blue and orange shows theshow lines change in the the actual upper andinventory lowerratio of product limits A. of the range, respectively, and the yellow line shows the change in the actual inventory ratio of product A. 5. Conclusions In this study, based on the premise of selling at fixed price, we tested an approach for reducing waste from unsold products in the textile and apparel industry and, thereby, mitigating adverse effects on the environment. The purpose of shipping personnel in the study is to recognize relevant data about sales situations and make appropriate judgments (i.e., predictions) about whether to issue alerts. The alerts in this paper are made from the result of data analysis to the product that shipping personnel should watch sales situation carefully. Although there are many kinds of data that can be
Sustainability 2019, 11, 259 12 of 14 When using the results of prediction, first, the shipping personnel would compare the conditional expectation with the inventory ratio of the product at the present moment. This shows how the inventory ratio of the product changes with respect to the average. Then, the shipping personnel would plan the shipping for the next week. Finally, they would determine the amounts of the shipment while also taking into account the sales policy. Also, the results of this prediction lead to different recommendations depending on the type of product. For example, in the case of a standard product, manufacturers sell for a longer term, so if the inventory runs out earlier than forecasted, it is possible to produce additional products to meet customer demand. On the other hand, in the case of a product sold for only one season, when the expected value of the stock ratio at the ninth week is large, this is a signal that products are not selling well that should be heeded by shipping personnel. In QR strategy in the logistics warehouse, product shipping quantities are decided at the time when shipping personnel receive sales information on each product during the monitoring period. However, in this paper, we give a signal to shipping personnel that is based on the comparison of previous inventory transition for a similar product to the current inventory transition for the current product. Therefore, even if there is no arrival of sales information, shipping personnel can receive signals about shipping. In addition, this method is effective for all sales periods. 5. Conclusions In this study, based on the premise of selling at fixed price, we tested an approach for reducing waste from unsold products in the textile and apparel industry and, thereby, mitigating adverse effects on the environment. The purpose of shipping personnel in the study is to recognize relevant data about sales situations and make appropriate judgments (i.e., predictions) about whether to issue alerts. The alerts in this paper are made from the result of data analysis to the product that shipping personnel should watch sales situation carefully. Although there are many kinds of data that can be analyzed in this particular industry, we chose to focus on logistics warehouse data, examining stock points to assess changes in the warehouse inventory ratios. Since the total quantities of apparel products varied considerably, the data was normalized in our study. Furthermore, because it was difficult to monitor the status of each individual product, we categorized products into several groups using cluster analysis. We found that the products whose sales information required the most careful monitoring were products that were sold in stages. For these products, we also forecasted inventory ratios using cluster results, and predictions showed that some products were more likely to remain unsold. Given this, we considered the products whose shipment patterns (i.e., timing and quantities) should be modified. This study has practical value for shipping personnel. By using conditional probability in the manner we have proposed, shipping personnel could accurately predict inventory ratios at the ninth week from changes in the inventory ratios up to the third week. Therefore, at the third week, shipping personnel could take remedial measures for products predicted to have excess inventory in the logistics warehouse. In light of the trade-off between the risk of disposal from unsold product and the risk of opportunity loss from product shortage, future research should investigate optimal shipment timing when disposal and shortage are simultaneously taken into consideration. Also, the optimal shipping quantities should be obtained at the optimum shipment timing. In practice, however, the timing or quantities of products shortage cannot be obtained as data. Therefore, under the assumption of a product shortage situation, the risk of opportunity loss will be evaluated. In addition, future research should verify the effectiveness of the proposed method by performing analyses in several different scenarios. In sum, using past data as well as current sales data can allow for better detection of market trends. Although the larger the amount of data, the easier it is to detect market trends in past and present, to do so, many textile and apparel companies are needed to share and analyze data. Apparel and textile companies can use our findings to improve the timing and quantity of shipments,
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