Forecasting Demand for Services
Learning Objectives l Recommend the appropriate forecasting model for a given situation. l Conduct a Delphi forecasting exercise. l Describe the features of exponential smoothing. l Conduct time series forecasting using exponential smoothing with trend and seasonal adjustments.
Forecasting Models l Subjective Models Delphi Methods l Causal Models Regression Models l Time Series Models Moving Averages Exponential Smoothing
Delphi Forecasting Question: In what future election will a woman become president of the united states?
N Period Moving Average Let : MA T = The N period moving average at the end of period T A T = Actual observation for period T Then: MA T = (A T + A T-1 + A T-2 + …..+ A T-N+1 )/N Characteristics: Need N observations to make a forecast Very inexpensive and easy to understand Gives equal weight to all observations Does not consider observations older than N periods
Moving Average Example Saturday Occupancy at a 100-room Hotel Three-period Saturday Period Occupancy Moving Average Forecast Aug Sept
Exponential Smoothing Let : S T = Smoothed value at end of period T A T = Actual observation for period T F T+1 = Forecast for period T+1 Feedback control nature of exponential smoothing New value (S T ) = Old value (S T-1 ) + [ observed error ] or :
Exponential Smoothing Hotel Example Saturday Hotel Occupancy ( =0.5) Actual Smoothed Forecast Period Occupancy Value Forecast error Saturday t A t S t F t |A t - F t | Aug Sept MAD = Mean Absolute Deviation (MAD)
Exponential Smoothing Implied Weights Given Past Demand Substitute for If continued:
Exponential Smoothing Weight Distribution Relationship Between and N (exponential smoothing constant) : N (periods in moving average) :
Saturday Hotel Occupancy Effect of Alpha ( =0.1 vs. =0.5) Actual Forecast
Exponential Smoothing With Trend Adjustment Commuter Airline Load Factor Week Actual load factor Smoothed value Smoothed trend Forecast Forecast error t A t S t T t F t | A t - F t | MAD 6.7
Exponential Smoothing with Seasonal Adjustment Ferry Passengers taken to a Resort Island Actual Smoothed Index Period t A t value S t I t Forecast F t | A t - F t| 1995 January … ….. February … ….. March … ….. April … ….. May … ….. June … ….. July … ….. August … ….. September … ….. October … ….. November … ….. December … January ….. February March April May
Topics for Discussion l What characteristics of service organizations make forecast accuracy important? l For each of the three forecasting methods, what are the developmental costs and associated cost of forecast error? l Suggest independent variables for a regression model to predict the sales volume for a proposed video rental store location. l Suggest how the Delphi method can be incorporated into a cross-impact analysis.