review use data table from quiz #4 to forecast sales using exponential smoothing, α = 0.2 what is...
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Review
Use data table from Quiz #4 to forecast sales using exponential smoothing, α = 0.2What is α called?
We are weighting the error associated with each time period by α1
Ft+1 = Ft + a(Yt – Ft)
Yt – Ft = et
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weekActual Sales
(# of units) Yt
Forecast Sales Ft
1 172 213 194 235 186 16
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Solve F2, F3, … F7 and e2, e3, … e6
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Use data table from Quiz #4 to forecast sales using simple linear regressionWe are using ONLY a time variable to
predict sales here!Predict future sales based on correlation
between time (X, independent variable) and sales (Y, dependent variable)
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Tt = b0 + b1t
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Regression StatisticsMultiple R 0.205R Square 0.042Adjusted R Square -0.197Standard Error 2.854Observations 6
ANOVAdf SS MS F
Regression 1 1.429 1.429 0.175Residual 4 32.571 8.143Total 5 34
Coefficients Standard Error t Stat P-valueIntercept 20 2.657 7.529 0.002week -0.286 0.682 -0.419 0.697
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Calculate MSE for the forecast, and calculate T7
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weekActual Sales
(# of units) Yt
Forecast Sales Ft
1 172 213 194 235 186 16
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Seasonal pattern no trend
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Year Quarter Sales1 1 1251 2 1531 3 1061 4 882 1 1182 2 1612 3 1332 4 1023 1 1383 2 1443 3 1133 4 804 1 1094 2 1374 3 1254 4 1095 1 1305 2 1655 3 1285 4 96
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Um
brel
la S
ales
Time Period
Ubrella Sales
Year 1 Year 2 Year 3 Year 4 Year 5
Seasonal pattern no trend
We are saying that umbrella sales are driven by seasonal variability with NO increasing or decreasing trend over time
Every year: 1st and 3rd quarters have moderate sales 2nd quarter has highest sales 4th quarter has lowest sales
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Seasonal pattern no trend
If we are using a linear trend to forecast (simple linear regression), we can introduce “season” as a independent categorical variables (X’s)
In statistics, a categorical variable is a variable that can take on a very limited, fixed number of possible values
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Seasonal pattern no trend
If k = the # of categories, you will need k – 1 dummy variables
Since there are four seasons (4 categories), we need three dummy variables Qtr1 = 1 if Quarter 1, 0 otherwiseQtr2 = 1 if Quarter 2, 0 otherwiseQtr3 = 1 if Quarter 3, 0 otherwise
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Seasonal pattern no trend
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Year t Quarter Yt Q1 Q2 Q31 1 1 125 1 0 01 2 2 153 0 1 0 Regression Statistics1 3 3 106 0 0 11 4 4 88 0 0 02 5 1 118 1 0 02 6 2 161 0 1 02 7 3 133 0 0 12 8 4 102 0 0 03 9 1 138 1 0 03 10 2 144 0 1 03 11 3 113 0 0 13 12 4 80 0 0 04 13 1 109 1 0 04 14 2 137 0 1 04 15 3 125 0 0 14 16 4 109 0 0 05 17 1 130 1 0 05 18 2 165 0 1 05 19 3 128 0 0 15 20 4 96 0 0 0
Yt is the dependent variableQ1, Q2, Q3 are the independent, predictor variables
Dummy or categoricalvariables for seasonal Effects
Q1 = 1 if quarter = 1,otherwise Q1 = 0
Q2 = 1 if quarter = 2,otherwise Q2 = 0
Q3 = 1 if quarter = 3,otherwise Q3 = 0
Q4 = 0
Seasonal pattern no trend
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Regression StatisticsMultiple R 0.894R Square 0.799Adjusted R Square 0.761Standard Error 11.325Observations 20
ANOVAdf
Regression 3Residual 16Total 19
CoefficientsIntercept 95Q1 29Q2 57Q3 26
Seasonal pattern no trend
What is our model?
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Seasonal pattern no trend
Predict sales in each quarter of year 6 using the model
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Seasonal pattern with trend
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SalesYear Season Tie Sales
1 1 18562 20123 985
2 1 19952 21683 1072
3 1 22412 23063 1105
4 1 22802 24083 1120
Seasonal pattern with trend
We are saying that tie sales are driven by seasonal variability and that there is an increasing trend in sales over time
Every year: Sales are lowest – by far – in 3rd season Sales are highest in 1st season
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Seasonal pattern with trend
3 seasons or 3 categories ( k = 3) require the use of 2 dummy variables (k – 1)Seas1t = 1 if Season 1 in time period t, 0
otherwiseSeas2t = 1 if Season 2 in time period t, 0
otherwise We will also need a time variable to address
the trend over time
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Seasonal pattern with trend
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Year Season Sales S1 S2 Time1 1 1856 1 0 1
2 2012 0 1 23 985 0 0 3
2 1 1995 1 0 42 2168 0 1 53 1072 0 0 6
3 1 2241 1 0 72 2306 0 1 83 1105 0 0 9
4 1 2280 1 0 102 2408 0 1 113 1120 0 0 12
Dummy or categoricalvariables for seasonal Effects
S1 = 1 if season = 1,otherwise S1 = 0
S2 = 1 if season = 2,otherwise S2 = 0
Time period variable
Seasonal pattern with trend
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Regression StatisticsMultiple R 0.994R Square 0.987Adjusted R Square 0.983Standard Error 73.086Observations 12
ANOVAdf
Regression 3Residual 8Total 11
CoefficientsIntercept 797S1 1095.433S2 1189.467Time 36.467
Seasonal pattern no trend
What is our model?
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Seasonal pattern no trend
Predict sales in each season of year 5 using the model
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