Dear R Help,
Does anyone know off-hand the syntax for a bivariate (two-outcome) lme?
It's straightforward to fit a standard random-intercept random-slope model
to each of the two outcome variables:
lme(Y~X,random=list(ID=~X)...)
lme(Z~X,random=list(ID~X)...)
But it would be nice to fit the data (Y,Z) against X so that I can obtain
estimates of the correlation between the slopes and the intercepts; the
measurement errors are also different, so I'd need to use weights as well.
On a slightly more advanced level, let's assume that there is no
correlation between the intercept and the slope for the two outcome
variables, but that fluctuations about a linear trend are correlated. What
kinds of techniques can be used to estimate the correlation in fluctuations?
Best
Simon
Simon D.W. Frost, M.A., D.Phil.
Department of Pathology
University of California, San Diego
Antiviral Research Center
150 W. Washington St., Suite 100
San Diego, CA 92103
USA
Tel: +1 619 543 8080 x275
Fax: +1 619 298 0177
Email: sdfrost at ucsd.edu
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