 mixed models
(LCLMM) also known as growth mixture models or heterogeneous linear mixed
models.  The LCLMM consists in assuming that the population is divided in a
finite number of latent classes. Each latent class is characterised by a
specific trajectory modelled by a class-specific linear mixed model.  Both
the latent class membership and the trajectory can be explained according to
covariates.  This function is limited to a mixture of Gaussian outcomes. For
other types of outcomes, please see function l