I figure this might be of interest to some. Under New Features for version 2.0.1 NEW FEATURES by longstanding request, lme4 now allows users to specify structured covariance matrices, by tagging the covariance term (e.g. cs(1 + f | g) fits a compound symmetric covariance matrix, diag(...) fits a diagonal covariance matrix). See ?"Covariance-class" or vignette("covariance_structures", package = "lme4") for more detail https://lme4.r-universe.dev/lme4/NEWS Also, see "Covariance Structures" at https://lme4.r-universe.dev/articles/lme4/covariance_structures.html submitted by /u/Michigan_Water [link] [comments]