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james posted on Tuesday, February 17, 2009  11:47 am



Hi, I have a question regarding the input on slide 61 of your 2005 Growth Modeling Short Course Handout: Title is input for LSAY linear growth model without covariates. I'm confused as to what the following statement specifies under the i BY math7math10 and s BY math7@0 etc... [math7math10@0]; [i s]; This input is for growth modeling across 4 times points with single indicators. 


The i BY statement defines the intercept growth factor. The s BY statement defines the slope growth factor. The statement [math7math10@0]; fixes the intercepts of the outcomes at zero which is part of the growth model parametrization. The statement [i s]; frees the means of the intercept and slope growth factors. 

JM posted on Wednesday, February 18, 2009  3:34 pm



Thanks for your previous post  very helpful. I have another question (sorry!). I'm running an LGM regressing the i and s on a covariate. When I regressed one of my covariates onto both the i and s, I got a significant positive effect on the intercept, and a significant, negative estimate (est: 0.127 est/S.E. 2.149) on the slope. Does this mean that the higher the score on my covariate, the higher the initial level, and then the faster the drop in growth overtime? Or is it the slower the the drop in growth overtime? It is the result on the slope I want to double check. Thank you thank you!! 


The growth factors i and s are continuous variables. The regression coefficients in the regression of i and s on a covariate are linear regression coefficients. The interpretation is that for a one unit change in x, i and s change the amount of the regression coefficient. In one case the change is positive and in the other it is negative. 

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