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roshanm
Calcite | Level 5

I have a non-normal data. Do I need to make it normal (by appropriate transformation) prior to "Proc mixed" with "random" statement?

6 REPLIES 6
SteveDenham
Jade | Level 19

If you know the distribution from which the data is generated, then PROC GLIMMIX will suit your needs.  Unusual links (transformations) can be handled programmatically.

If you are determined to use PROC MIXED, then the key is making the RESIDUALS normal.  For instance, a bimodal distribution due to sex can never be made "normal" and the analysis does not require that the response variable be normal--only that the residuals be normally and identically distributed.

Steve Denham

Ksharp
Super User

Fisher's Z transform could help you to normalize it .

z=1/2* log( (1+x)/(1-x) )

Babloo
Rhodochrosite | Level 12

Any possibilities to provide me an example of Fisher's Z transform?

Babloo
Rhodochrosite | Level 12

Seems Fisher's Z transform is part of correlation. Will it work for single variable?

Ksharp
Super User

Yeah. I think it should be worked on a single variable. It is just a transform function . But I don't how good it is, You can test it.

Of course. Don't forget try to use LOG() to make the variable normal too.

SteveDenham
Jade | Level 19

Fisher's Z really only transforms values that are bounded below by -1 and above by 1 into normal deviates.

Steve Denham

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