hello. I am planning to use a mixed model when writing my paper. I have three questions:
1. When controlling covariates such as age, years of education, and gender, it is said that gender is treated as a dummy variable because it is nominal. What about age or years of education? Can I check centered?
2. When the level 2 independent variable is a group, mean centering cannot be performed, so can it be treated as a dummy variable in this case as well?
3. When I want to add covariates, is it correct to put the nominal variables in factors and the rest in covariates?
thank you for your help
have a good day.
mean centering & variables scaling
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Re: mean centering & variables scaling
1. sure, that is the default. With mixed model is always a good idea to center the covariates (although not necessary)
2. any factor is transformed in contrast variables and their coding is mean-centered (if do not select "dummy" as a coding system)
3. yes
2. any factor is transformed in contrast variables and their coding is mean-centered (if do not select "dummy" as a coding system)
3. yes