unit 15 - trend/seasonal variation help

lisnic

ok i have 1 additional question to do on my unit 15 sim - i knew i had trashed this question!!! everything else on my feedback was pretty perfect!

ive been told it will be a totally different question wont be asked to do the same question again

ive looked in my notes as the sheet i received said revise trends and seasonal variations when you are given actual figures (ie sales) and the seasonal variations and asked to work out the trend and then forecasting future figures

how to i do i do this as in my notes i cant see any examples or anything doing as such?? i asked the marker where i went wrong and all i could be told was that id tried to do a moving average when infact it was a much simpler calculation

also i take it it will be the same sort of question asking similar to what was in sim not something totally different?

not great timng doing this tomorrow and 2 exams next week so having to stop my exam study for a morning today ahhh!

Bookworm55

ive looked in my notes as the sheet i received said revise trends and seasonal variations when you are given actual figures (ie sales) and the seasonal variations and asked to work out the trend and then forecasting future figures

how to i do i do this as in my notes i cant see any examples or anything doing as such?? i asked the marker where i went wrong and all i could be told was that id tried to do a moving average when infact it was a much simpler calculation

A much simpler calculation? I'm not 100% sure, but I have a hunch about what he was getting at.

What you have is two sets of figures: one for actual sales and one for the amount of seasonal variation, right? I think what you're supposed to do is subtract the seasonal variation from the actual sales for each month/week/quarter to give a deseasonalised sales figure (caution: may not be the right name).

Then you use the new figure to find a trendline without the seasonal figures getting in the way.

eg
Actual: 1Q: 9000 units 2Q: 9000 units 3Q: 5000 units: 4Q: 7000 units
Seasonal: 1Q: +5000 units 2Q: +4000 units 3Q: -1000 units: 4Q: +0 units
Deseasonal: 1Q: 4000 units 2Q: 5000 units 3Q: 6000 units: 4Q: 7000 units

Sorry, I couldn't get that to line up better,but if you look I've taken the seasonal variation off the actual sales, to give a deseasonal figure. You can tell from this that sales are increasing by 1000 units per quarter, which you couldn't tell from the actual figures.

lisnic

yeah i see that

so what would i then to forecast if say the last known figures are 2 or 3 quarters behind where i need to start my forecast