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Basics. Same underlying causal system that existed in past will continue.Aggregate Forecast are better than disaggregate ones.Forecast accuracy decreases as time horizon decreases.. Approaches to Forecasting. Judgmental ForecastsSubjective inputs from various sourcesConsumer surveys
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1. Forecasting Models Static vs. Dynamic
2. Basics
3. Visual Investigation
4. Static Model , Simple Average Basic Assumption: No change in demand, all fluctuations are random.
Forecast = Average
A measure of match between forecast and actual data is MAD
= Mean Absolute Deviation
= Average (absolute value of (sales-forecast) for the overall data range)
5. Static Model – Modeling Trend Assumption : There is a linear trend in data.
Plot the data and add trend line (linear).
Intercept
Slope = Trend
First Period Forecast = Intercept + Trend
Forecast = Previous period forecast + Trend
6. Static Model with SeasonalitySeasonality*(Linear Trend)
7. Dynamic Model – Exponential Smoothing
8. Exponential Smoothing with Trend First Period Forecast
= Intercept + Slope (from trendline)
Next Period Forecast
Average = (1-a)Previous Forecast + a*Previous Sales
Slope = b* D in Averages +(1-b)*Previous Trend
Forecast = Average +Trend
To incorporate seasonality multiply forecast with seasonality factor.