ke account of these unobserved, but important, taxa.
In order to account for the estimated nature of the response, a mixed model
approach is taken, whereby the varying levels of confidence in the estimates
contributes to a diagonal but heteroscedastic covariance matrix. Given
covariates constitute the fixed effects in the mixed model, and significance
of the random effect term ``sigsq_u'' reflects heterogeneity in the sample,
that is, variability that cannot be explained by only the covariates. The
authors 