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Prefmap number of products

By Alard Verhoef | Apr 17, 2018 03:31PM CEST

Deal XLSTAT,

Ik would like to know how many products I need include in order to run a prefmap analysis. I tried doing it with 6 but it says too little observations. The tutorial is done with 10. I was unaware that there was a minimum amount of products required, it is not mentioned anywhere. Is there room for me to work around this?

Kind regards,
Alard

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By Sébastien | Apr 17, 2018 05:16PM CEST | XLSTAT Agent

Hello,

It is a question of degree of freedom.
For example, a quadratic model with 2 dimensions (F1, F2) will consume 5 DF (Intercept+ F1 + F2 +F1^2 +F2^2)

The degree of Freedom for the explained model is given by k, where k = number of independent variables in the regression equation. For the residual, the error unexplained by the regression model, the degree of freedom is given by (n-k-1), where n = number of counts of the independent variable in the dataset.

n-k-1 shall be positive so if you take n=6 then DF of residual becomes null which is not good into calculating the estimate.

Regards

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