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Published byGeoffrey Benton Modified over 3 years ago

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FITTING TREND LINES AND FORECASTING

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FITTING BY EYE: inadequate technique. We will look at the following two: 3-MEDIAN METHOD AND LEAST-SQUARES REGRESSION

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Only works for the following original data: 1. When trend is clearly linear 2. Random 3. Secular (increasing or decreasing) Does not work on: 1. Cyclical trends 2. Seasonal trends

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STEP 1: STATS - LIST 1: TIME - LIST 2: INDEPENDENT VARIABLE STEP 2: SET GRAPH - SETTING -TYPE: SCATTER - LIST 1: TIME - LIST 2: INDEPENDENT VARIABLE - SET STEP 3: CALC -LINEAR REG - LIST 1: TIME - LIST 2: INDEPENDENT VARIABLE - COPY FORMULA: y1 STEP 4: FORCASTING - y1 (x) -EXE

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The y-intercept: when time code is at 0, please be careful and consider what the data is about. Eg: Our last example, the y- intercept is the day before the opening of the salon. This has no real meaning. The gradient (rate of change): very important. Eg: growing by approx 2 customers per day.

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EXERCISE 4B pg 163 Q’s 1-10

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MEDIAN SMOOTHING. Smoothing involves replacing the original time series with another one where most of the variation has been removed, in order to see.

MEDIAN SMOOTHING. Smoothing involves replacing the original time series with another one where most of the variation has been removed, in order to see.

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