In an answer to Antoine PACCARD at 12 November (lme/lmer and random effects correlation parameters<http://news.gmane.org/find-root.php?message_id=%3c6C50350B%2d8BC6%2d427B%2dBEF0%2dCB2B2AD1A506%40unine.ch%3e>):

> lmer will work and converge properly.

Ben Bolker stated:

I would be very careful about this statement.  Are you *sure* it
has converged properly?  Do the results make sense?  Do you get
non-trivial (not zero, not very very small, correlations not
equal to +/- 1.0) estimates for the variance-covariance matrix?

I recently got +1 for one (random effects) correlation in a four times four correlation matrix from lmer(). From my raw data, it is reasonable that the two parameters under consideration are closely and positively correlated. Further, the fixed estimates, their standard errors and remaining random effects correlation parameters seem to be reasonable (these ranged from -0.55 to +0.85). So, what specifically is the problem with correlations being close to 1 or 1.0, or being close to 0 or zero?

I appreciate your time.

Matthias Suter,
Agroscope Reckenholz-Tänikon ART, Zürich


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