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In mixed models that I'm familiar with, the DV is a continuous repeated variable (for example, anxiety measured a few times), and the IV is a factorial variable (for example, gender). Is it possible to use a IV that is a continuous variable (for example, age)?

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The short answer is "Yes".

The long answer will depend on how you are fitting you mixed model (and what you mean by mixed model), what software you are using, etc.

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  • $\begingroup$ Thanks! Mixed model= 1 between (IV) variable and 1 within (DV) variable. I prefer SPSS but R is possible also. $\endgroup$ Sep 22 '17 at 17:27
  • $\begingroup$ @user3315563, I have not used SPSS in quite a while, so have no advice there. In R I would use the "lme4" package which does what you want directly. $\endgroup$
    – Greg Snow
    Sep 22 '17 at 17:39
  • $\begingroup$ thanks again. But is it possible to run MLM with a contiguous IV (such as age)? $\endgroup$ Sep 23 '17 at 14:12
  • $\begingroup$ @user3315563, Yes. In R using the lme4 package the syntax would be something like: fit <- lmer( anxiety ~ age + (1|subject), data=anx.data) and that will fit a multi-level model with continuous age (well as continuous as a computer will do) with separate intercepts for each subject. You will need to match the code to your actual data and should really read the documentation for details. I have no idea how to do this in SPSS. $\endgroup$
    – Greg Snow
    Sep 25 '17 at 15:21

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