[R] converting a t statistic to r2

From: Shaw, Philip (NIH/NIMH) <shawp_at_mail.nih.gov>
Date: Sat 13 Aug 2005 - 06:49:55 EST


HI  

I wonder if anyone can help. I have a longitudinal sample of 100 subjects: 200 data points were acquired starting at different ages and at irregular intervals (subjects have different numbers of repeated data points, so some have only one data point). I have been examining the relationship over time (it is quadratic) of continuous variables A on variable B. To model this I have been using linear mixed models in R.  

B~A*age +A*I(age^2) + random term (for individual)  

I get t values associated with A, age and A*age.  

How (or can) the t value for A be converted to a correlation (r) or variance value?  

I recall that R2 = t2/(df+t2)  

But can this be applied to linear mixed models and what are the degrees of freedom?  

I hope this is reasonably clear,  

Many thanks for any opinions  

Philip  

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