Nesting in a Mixed Model, Fixed or Random

[S Battersby]

Hi all,

I’m using a Mixed Model at the moment and I have a question regarding a factor and if it should be fixed or random.

It makes use of two factors: Condition (Fixed) and Group (Random). I want to include Condition x Group. Now, does this mean that this nested factor becomes a Random factor because of Group, or is it still Fixed because of Condition?

I’m using SPSS 18.

Many Thanks,
S.

[Jeremy Miles]

Random and fixed are very curious terms that mean different things in different contexts. (For example, if you want to run what an economist calls a fixed-effects regression, you need to put a random factor into a mixed model. But if you want to run a random effects regression, you can use regression, or mixed model with no random factors).

Tell us more about your design.

Jeremy

[Author]

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