【正文】 y Management 79 Optimal inventory policy assumes a specific service level target. What is the appropriate level of service? – May be determined by the downstream customer Retailer may require the supplier, to maintain a specific service level Supplier will use that target to manage its own inventory – Facility may have the flexibility to choose the appropriate level of service Service Level Optimization Inventory Management 80 Service Level Optimization Service level inventory versus inventory level as a function of lead time Inventory Management 81 TradeOffs Everything else being equal: – the higher the service level, the higher the inventory level. – for the same inventory level, the longer the lead time to the facility, the lower the level of service provided by the facility. – the lower the inventory level, the higher the impact of a unit of inventory on service level and hence on expected profit Inventory Management 82 Retail Strategy Given a target service level across all products determine service level for each SKU so as to maximize expected profit. Everything else being equal, service level will be higher for products with: – high profit margin – high volume – low variability – short lead time Inventory Management 83 Risk Pooling: Important Observations Centralizing inventory control reduces both safety stock and average inventory level for the same service level. The higher the coefficient of variation, the greater the benefit obtained from centralized systems. The benefits from risk pooling depend on the behavior of demand from one market relative to demand from another. (negatively correlated demand) Inventory Management 84 Centralized versus Decentralized Systems ― The Tradeoffs Safety stock: lower with centralization Service level: higher service level for the same inventory investment with centralization Overhead costs: higher in decentralized system Customer lead time: response times lower in the decentralized system Transportation costs: not clear. Consider outbound and inbound costs. Inventory Management 85 Managing inventory in the supply chain1 考慮一個(gè) 多設(shè)施的供應(yīng)鏈 ，並屬於 同一家公司 。公司的 目的 在 管理其存貨以降低整體系統(tǒng)成本 ；因此 考慮不同設(shè)施間的互動(dòng)及這些互動(dòng)對(duì)每個(gè)設(shè)施應(yīng)採取存貨政策的影響是很重要的。 二項(xiàng)重要且合理的假設(shè)： 1. 存貨決策由單一決策者制訂 ，且這決策者的目標(biāo)是使整體系統(tǒng)成本減到最小 。 2. 決策者有 獲取各零售商和倉庫存貨資訊 的管道。 Inventory Management 86 Managing inventory in the supply chain2 在這些假設(shè)下，存貨政策是根據(jù)所謂 階層存貨 (echelon inventory)進(jìn)行存貨管理 ， 是一個(gè)有效的存貨管理系統(tǒng)。 在配銷系統(tǒng)中，每一階段或?qū)蛹?jí) (亦即倉庫或零售商 )被視為一階層 (echelon)。 因此，這系統(tǒng)中， 任何階段或?qū)蛹?jí)的階層存貨(echelon inventory)等於此階層中現(xiàn)有的存貨，再加上所有的下游存貨(downstream inventory)。 Inventory Management 87 Managing inventory in the supply chain3 Echelon inventory position – The echelon inventory at the echelon, plus those items ordered by the echelon that have not yet arrived minus all items that are backordered. Inventory Management 88 The warehouse echelon inventory1 Supplier Warehouse Retailers Warehouse echelon lead time Inventory Management 89 The warehouse echelon inventory2 The reorder point of warehouse is ees L A V G z S T D L? ? ? ?Where Le=echelon lead time, defined as the lead time between the retailers and the warehouse plus the lead time between the warehouse and its supplier AVG=average demand across all retailers STD=standard deviation of demand across all retailers Inventory Management 90 Inventory Management: Best Practice Periodic inventory reviews Tight management of usage rates, lead times and safety stock (the smaller variation) ABC approach Reduced safety stock levels Shift more inventory, or inventory ownership, to suppliers Quantitative approaches Inventory Management 91 Inventory Turnover Ratio Inventory turnover ratio = annual sales/avg. inventory level Increase in inventory turnover leads to – Decrease in average inventory levels – Higher level of liquidity – Smaller risk of obsolescence – Reduced investment in inventory – Increases the risk of lost sales Inventory Management 92 Indus tr y Upper Quart ile Medi an Low er Quart ile Dair y Product s Electronic Com ponent Electronic Com puters Books: publis hing Household audio amp。 video equipment Household electrical appliance s Industrial chem ical Inventory Turnover Ratio Inventory Management 93 Factors that Drive Reduction in Inventory Top management emphasis on inventory reduction (19%) Reduce the Number of SKUs in the warehouse (10%) Improved forecasting (7%) Use of sophisticated inventory management software (6%) Coordination among supply chain members (6%) Others Inventory Management 94 Forecasting General Overview: – Judgment methods – Market research methods – Time Series methods – Causal methods Inventory Management 95 Judgment Methods1 Assemble the opinion of experts Salesforce posite bines salespeople’s estimates –優(yōu)點(diǎn) 銷售員直接與顧客接觸，較能知道顧客對(duì)於未來的考量與計(jì)畫。 –缺點(diǎn) 銷售員無法區(qū)分顧客想做與實(shí)際會(huì)做的事。 銷售員易過度受到最近經(jīng)驗(yàn)的影響。 Inventory Management 96 Judgment Methods2 Panels of experts – internal, external, both Delphi method – Each member surveyed – Opinions are piled – Each member is given the opportunity to change his opinion Inventory Management 97 Market Research Methods Particularly valuable for developing forecasts of newly introduced products Market testing – Focus groups assembled. – Responses tested. – Extrapolations to rest of market made. Market surveys – Data gathered from potential customers – Interviews, phonesurveys, written surveys, etc. Inventory Management 98 Time Series Methods Past data is used to estimate future data Examples include – Moving averages – average of some pre