【正文】 generally, more forecast accuracy can be obtained at a cost. ? Highaccuracy approaches have disadvantages: ? Use more data ? Data are ordinarily more difficult to obtain ? The models are more costly to design, implement, and operate ? Take longer to use 80 Criteria for Selecting a Forecasting Method ? Cost and Accuracy ? Low/ModerateCost Approaches – statistical models, historical analogies, executivemittee consensus ? HighCost Approaches – plex econometric models, Delphi, and market research 81 Criteria for Selecting a Forecasting Method ? Data Available ? Is the necessary data available or can it be economically obtained? ? If the need is to forecast sales of a new product, then a customer survey may not be practical。 instead, historical analogy or market research may have to be used. 82 Criteria for Selecting a Forecasting Method ? Time Span ? What operations resource is being forecast and for what purpose? ? Shortterm staffing needs might best be forecast with moving average or exponential smoothing models. ? Longterm factory capacity needs might best be predicted with regression or executivemittee consensus methods. 83 Criteria for Selecting a Forecasting Method ? Nature of Products and Services ? Is the product/service high cost or high volume? ? Where is the product/service in its life cycle? ? Does the product/service have seasonal demand fluctuations? 84 Criteria for Selecting a Forecasting Method ? Impulse Response and Noise Dampening ? An appropriate balance must be achieved between: ? How responsive we want the forecasting model to be to changes in the actual demand data ? Our desire to suppress undesirable chance variation or noise in the demand data 85 Reasons for Ineffective Forecasting ? Not involving a broad cross section of people ? Not recognizing that forecasting is integral to business planning ? Not recognizing that forecasts will always be wrong ? Not forecasting the right things ? Not selecting an appropriate forecasting method ? Not tracking the accuracy of the forecasting models 86 Monitoring and Controlling a Forecasting Model ? Tracking Signal (TS) ? The TS measures the cumulative forecast error over n periods in terms of MAD ? If the forecasting model is performing well, the TS should be around zero ? The TS indicates the direction of the forecasting error。1 1 2 0 0 2 So u t h W e st e rn / T h o mso n L e a rn i n g TMS l i d e s p r e p a r e db y J o h n L o u c k s2 Chapter 3 Demand Forecasting 3 Overview ? Introduction ? Qualitative Forecasting Methods ? Quantitative Forecasting Models ? How to Have a Successful Forecasting System ? Computer Software for Forecasting ? Forecasting in Small Businesses and StartUp Ventures ? WrapUp: What WorldClass Producers Do 4 Introduction ? Demand estimates for products and services are the starting point for all the other planning in operations management. ? Management teams develop sales forecasts based in part on demand estimates. ? The sales forecasts bee inputs to both business strategy and production resource forecasts. 5 Forecasting is an Integral Part of Business Planning Forecast Method(s) Demand Estimates Sales Forecast Management Team Inputs: Market, Economic, Other Business Strategy Production Resource Forecasts 6 Some Reasons Why Forecasting is Essential in OM ? New Facility Planning – It can take 5 years to design and build a new factory or design and implement a new production process. ? Production Planning – Demand for products vary from month to month and it can take several months to change the capacities of production processes. ? Workforce Scheduling – Demand for services (and the necessary staffing) can vary from hour to hour and employees weekly work schedules must be developed in advance. 7 Examples of Production Resource Forecasts Long Range Medium Range Short Range Years Months Days, Weeks Product Lines, Factory Capacities Forecast Horizon Time Span Item Being Forecasted Unit of Measure Product Groups, Depart. Capacities Specific Products, Machine Capacities Dollars, Tons Units, Pounds Units, Hours 8 Forecasting Methods ? Qualitative Approaches ? Quantitative Approaches 9 Qualitative Approaches ? Usually based on judgments about causal factors that underlie the demand of particular products or services ? Do not require a demand history for the product or service, therefore are useful for new products/services ? Approaches vary in sophistication from scientifically conducted surveys to intuitive hunches about future events ? The approach/method that is appropriate depends on a product’s life cycle stage 10 Qualitative Methods ? Educated guess intuitive hunches ? Executive mittee consensus ? Delphi method ? Survey of sales force ? Survey of customers ? Historical analogy ? Market research scientifically conducted surveys 11 Quantitative Forecasting Approaches ? Based on the assumption that the “forces” that generated the past demand will generate the future demand, ., history will tend to repeat itself ? Analysis of the past demand pattern provides a good basis for for