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                      Forecasting Methods

                                                           

 Forecasting Methods Assignment   

Shivanand R. Koppalkar

University of Phoenix

MGT 554: Operations Management 

Steven Williams

August 28, 2006


Introduction

Forecasting can be defined as Estimating or predicting future events or conditions. Forecasts may be long-term or short-term. The techniques used may be quantitative (often making sue of computers) or qualitative. Quantitative forecasting models may be classified into (a) causal models in which independent variables are used to forecast dependent variables, and (b) time series models, which produce forecasts by extrapolating the historical values of the variables of interest by, e.g., moving averages.

Seasonal Model

Seasonality is a pattern that repeats for each period. For example annual seasonal pattern has a cycle that is 12 periods long, if the periods are months, or 4 periods long if the periods are quarters. The seasonal index is required to be found for each month, or other periods, such as quarter, week depending on the data availability (Hossein, 1994-2006).

Seasonal Index:

Seasonal index represents the extent of seasonal influence for a particular segment of the year. The calculation involves a comparison of the expected values of that period to the grand mean. A seasonal index is how much the average for that particular period tends to be above (or below) the grand average. Therefore, to get an accurate estimate for the seasonal index, compute the average of the first period of the cycle, and the second period and divide each by the overall average (Hossein, 1994-2006). The formula for computing seasonal factors is:

Si = Di/D,

Where:
S
i = the seasonal index for ith period,
D
i = the average values of ith period,
D = grand average,
i = the i
th seasonal period of the cycle.

A seasonal index of one for a particular month indicates that the expected value of that month is 1/12 of the overall average. A seasonal index of 1.25 indicates that the expected value for that month is 25% greater than 1/12 of the overall average. A seasonal index of 80 indicates that the expected value for that month is 20% less than 1/12 of the overall average (Hossein, 1994-2006).

Deseasonalizing Process

Deseasonalizing the data, also called Seasonal Adjustment is the process of removing recurrent and periodic variations over a short time frame, e.g., weeks, quarters, months. Therefore, seasonal variations are regularly repeating movements in series values that can be tied to recurring events. The Deseasonalized data is obtained by simply dividing each time series observation by the corresponding seasonal index (Hossein, 1994-2006).

Almost all time series published by the US government are already deseasonalized using the seasonal index to unmasking the underlying trends in the data, which could have been caused by the seasonality factor (Hossein, 1994-2006).

Forecasting

Incorporating seasonality in a forecast is useful when the time series has both trend and seasonal components. The final step in the forecast is to use the seasonal index to adjust the trend projection. One simple way to forecast using a seasonal adjustment is to use a seasonal factor in combination with an appropriate underlying trend of total value of cycles (Hossein, 1994-2006).

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Technological Forecasting Model

Technological forecasting is a subset of futures research. Futures research is an umbrella term which encompasses "any activity that improves understanding about the future consequences of present developments and choices" (Amara and Salanik, 1972, p. 415). In defining forecasting, the authors offer the following progression. Forecasting is:

  1. A statement about the future,
  2. A probabilistic statement about the future:
  3. A probabilistic, reasonably definite statement about the future:
  4. A probabilistic, reasonably definite statement about the future, based upon an evaluation of alternative possibilities. (Amara and Salanik, 1972, p. 415)

Technological forecasting includes ...

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