Thu, 09/02/2010 - 16:22

Hello,

How do I specify the intercept and slope means for a growth curve, using an ACE parameterization.

I can follow the RAM notation for growth curves in the documentation, but I'm not sure how to specify the intercept and slope means outside of the RAM framework.

Maybe another way to ask the question is as such: In the ACE factor model examples (common pathway model) the factor means are fixed at zero. How can I change the code to estimate the factor mean?

Thanks,

Scott

It depends a bit on whether you are using path or matrix specification. With matrix specification, the algebra for the means simply needs to be changed to include a component which goes:

FacLoadings %*% FacMeans

where FacMeans is a vector of free parameters for the means of each common factor, and FacLoadings are the common pathway factor loadings. At the same time, it is necessary to remove (or fix at zero) the parameters that directly estimate the means of the observed variables.

Thanks, I had already tried just that but couldn't get it to work. For some reason my FacMeans weren't being estimated as free parameters. I'll take a closer look now that I know I was on the right track.

Thanks,

-Scott