Additive Seasonal lnfluencesYear 1Year 2Year 3QuarterYear 4145-250=-20570-300=-230100-450=-350100-550=-4502335-250=85370-300=70585-450=135725-550=1753520-250=270590-300=290830-450=3801160-550=6104100-250=-150170-300=-130285-450=-165215-550=-335QuarterAverageSeasonalIndexStep 2: For1(-205-230-350-450)/4=-308.75each quarter2=116.25(85+70+135+175)/4compute the3(270+290+380+610)/4=387.50average4(-150-130-165-335)/4=-195.00seasonal index
Quarter Average Seasonal Index 1 (-205-230-350-450)/4 = -308.75 2 (85+70+135+175)/4 = 116.25 3 (270+290+380+610)/4 = 387.50 4 (-150-130-165-335)/4 = -195.00 Additive Seasonal Influences Step 2: For each quarter compute the average seasonal index Quarter Year 1 Year 2 Year 3 Year 4 1 45-250 = -205 70-300 = -230 100-450 = -350 100-550 = -450 2 335-250 = 85 370-300 = 70 585-450 = 135 725-550 = 175 3 520-250 = 270 590-300 = 290 830-450 = 380 1160-550 = 610 4 100-250 = -150 170-300 = -130 285-450 = -165 215-550 = -335
Additive SeasonallnfluencesGiven projected average quarterly demand =650The quarterly demand forecasts are obtained as follows:QuarterAverage Seasonal IndexForecast1-308.75650-308.75=341.252116.25650+116.25=766.253387.50650+387.50=1037.504-195.00650-195.00=455.00
Additive Seasonal Influences Given projected average quarterly demand =650 The quarterly demand forecasts are obtained as follows: Quarter Average Seasonal Index Forecast 1 -308.75 650-308.75=341.25 2 116.25 650+116.25=766.25 3 387.50 650+387.50=1037.50 4 -195.00 650-195.00=455.00