Post on 09-Apr-2018
transcript
8/8/2019 08x02 Seasonally-Adjusted Forecasts
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Time-Series ForecastingUsing Microsoft Excel
Henry C. Co
Technology and Operations Management,
California Polytechnic and State University
Part 2. Seasonality-AdjustedForecasts
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Demand Forecasting (Henry C. Co)
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After completing the trendline inColumn E, lets add a column ofmoving averages.
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Step 1. Moving AverageMoving Average of 3 months
The center of the first 5-day moving average is the 3rd day i.e., cell D3 as
shown.
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Copy the formula in cell F4, and
paste it all the way to the
Wednesday of Week 7.
Notice that we did not copy the
formula beyond D34. Why?
The formula for D34, which is
D34=AVERAGE(D32:D36) uses
the last available demand data.
Beyond this cell, we would be
using blank cell for the movingaverage, which is not meaningful.
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Step 2. RatiosUse the demand data and the 5-period centered moving average to
determine the seasonal relatives.
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Copy the formula in cell G4, and
paste it all the way to the
Wednesday of Week 7.
Notice that we stopped at cell
G34.
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Step 3. Seasonal Relatives
Insert a column and label it "Seasonal Rel.Compute the seasonal relatives for :Wednesday by taking the average of all ratiocorresponding to Wednesdays Cell, i.e.,H4=AVERAGE(G4,G9,G14,G19,G24,G29,G34)
.
Thursday by taking the average of all ratio
corresponding to Thursday (Cell H5).
Friday by taking the average of all ratio corresponding toFriday (Cell H6).
Monday by taking the average of all ratio correspondingto Monday (cell H7).
Tuesday by taking the average of all ratio correspondingto Tuesday (Cell H8)
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Insert a column and label it "Seasonal Rel.
Compute the seasonal relatives for :
Wednesday by taking the average of all ratio
corresponding to Wednesdays Cell, i.e.,
H4=AVERAGE(G4,G9,G14,G19,G24,G29,G34).
Thursday by taking the average of all ratio
corresponding to Thursday , i.e.,
H5=AVERAGE(G5,G10,G15,G20,G25,G30)
Friday by taking the average of all ratio
corresponding to Friday , i.e.,
H6=AVERAGE(G6,G11,G16,G21,G26,G31.
Monday by taking the average of all ratio
correspond1ing to Monday , i.e.,
H7=AVERAGE(G7,G12,G17,G22,G27,G32)
Tuesday by taking the average of all ratiocorresponding to Tuesday , i.e.,
H8=AVERAGE(G8,G13,G18,G23,G28,G33.
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Click and drag to highlight the first 5 seasonal relatives.Then right-click and choose copy.
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Use "Paste Special" to paste the VALUES downwards (next 5 days)
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Repeat "Paste Special" to paste the VALUES, until you pass the last row
of data. (See next slide)
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This is a screenshot showing the 5 seasonal relatives copied passed the last row of data.
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Step 4. Adjusted ForecastedInsert a column and label it "ADJ Forecast"
The seasonally adjusted forecast = the value on the trendline * seasonal
relative.
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Copy the formula and
paste all the end of week8.
You may have to decreasethe decimal places.
The forecast for week 8 isshown in column I, rows37-41.