【正文】 are both smoothed. 76 Exponential Smoothing with Trend ? Model Form FTt = St1 + Tt1 where: FTt = forecast with trend in period t St1 = smoothed forecast (average) in period t1 Tt1 = smoothed trend estimate in period t1 77 Exponential Smoothing with Trend ? Smoothing the Average St = FTt + a (At – FTt) ? Smoothing the Trend Tt = Tt1 + b (FTt – FTt1 Tt1) where: a = smoothing constant for the average b = smoothing constant for the trend 78 Criteria for Selecting a Forecasting Method ? Cost ? Accuracy ? Data available ? Time span ? Nature of products and services ? Impulse response and noise dampening 79 Criteria for Selecting a Forecasting Method ? Cost and Accuracy ? There is a tradeoff between cost and accuracy。 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。 if the TS is positive increase the forecasts, if the TS is negative decrease the forecasts. nii1( A c tua l d em a n d For ec a s t d em a n d )T S = M A Di ??87 Monitoring and Controlling a Forecasting Model ? Tracking Signal ? The value of the TS can be used to automatically trigger new parameter values of a model, thereby correcting model performance. ? If the limits are set too narrow, the parameter values will be changed too often. ? If the limits are set too wide, the parameter values will not be changed often enough and accuracy will suffer. 88 Computer Software for Forecasting ? Examples of puter software with forecasting capabilities ? Forecast Pro ? Autobox ? SmartForecasts for Windows ? SAS ? SPSS ? SAP ? POM Software Libary Primarily for forecasting Have Forecasting modules 89 Forecasting in Small Businesses and StartUp Ventures ? Forecasting for these businesses can be difficult for the following reasons: ? Not enough personnel with the time to forecast ? Personnel lack the necessary skills to develop good forecasts ? Such businesses are not datarich environments ? Forecasting for new products/services is always difficult, even for the experienced forecaster 90 Sources of Forecasting Data and Help ? Government agencies at the local, regional, state, and federal levels ? Industry associations ? Consulting panies 91 Some Specific Forecasting Data ? Consumer Confidence Index ? Consumer Price Index (CPI) ? Gross Domestic Product (GDP) ? Housing Starts ? Index of Leading Economic Indicators ? Personal Ine and Consumption ? Producer Price Index (PPI) ? Purchasing Manager’s Index ? Retail Sales 92 WrapUp: WorldClass Practice ? Predisposed to have effective methods of forecasting because they have exceptional longrange business planning ? Formal forecasting effort ? Develop methods to monitor the performance of their forecasting models ? Do not overlook the short run.... excellent short range forecasts as well 93 End of Chapter 3