Check this option to allow
variance
component estimates to be
negative
for the
random effects
in your
model
.
This condition is appropriate when negative correlations between
observations
are reasonable, and can make fixed effect tests less biased.
Caution
: Selecting this option can prove considerably more computationally intensive than the default method, which constrains variance component estimates to be nonnegative.
Refer to the
SAS documentation for PROC MIXED
for more information.