Formula or Methodology used for Seasonal & Linear Regression Forecast Model

[Former Member]

Hi all,

I am using the Forecast Model 35 (Seasonal & Linear Regression Model) for Statistical Forecast generation.

Now I am facing the Issue that my Model 35 is consistently Under Forecasting.

Can anyone let me know what Formula or Logic is used by the Model to generate the Statistical Forecast.What are the Parameters that can really improve the Under Forecasting trend for Model 35.

kindly help...

Thanks & Regards,

Vishal.S.Pandya.

[srinivas_krishnamoorthy]

Couple of quick checks that you should do

1. Make sure there is no Like Profile active for that planning object that is interfering

2. Do a Strategy 56 to test for season and trend. See if streatgy 56 indeed recommends regression model

3. If strategy 56 fails for season or trend, and you enforce seasonal or linear regression model - i would expect to see the behaviour you are seeing

4. Make sure there are adequate time buckets for forecast initialization

5. Make sure the forecast initialization buckets are representative of the forecasts and are not outliers

IN this regard do check

http://help.sap.com/saphelp_scm50/helpdata/en/19/06f74ee2ed11d3b78d0000e82debc6/content.htm

http://help.sap.com/saphelp_scm50/helpdata/en/96/d261f8e39011d3b78e0000e82debc6/content.htm

[Former Member]

Hi Ian,

The same formula for Model 35 exist in APO help which I had already referred.

The Issue is that how does it calculate the Seasonal Index logically.

The basic logical understanding for the working of Model 35 is required which could reslove my doubts for instance what priority is to be assigned to the recent history or the impact of changing Alpha,Beta or Gamma factors on the working of the Model,Outliar correction method to be used or not ......

Thanks & regards,

Vishal.S.Pandya.

[Former Member]

Hi

SAP Help explains the model's formula quite nicely:

[Seasonal Linear Regression|http://help.sap.com/saphelp_scm50/helpdata/en/35/1b4839f6e76756e10000000a114084/content.htm]

May also be worth looking at Model 30 (Seasonal) if you think model 35 is underforecasting consistently.

Regards

Ian