I have a run a linear mixed effects model in R to model clinical data. However, however this model is heteroscedastic (as there excess zeros in the response variable)....
I have tried transforming the data (log transform) and (sqrt). Still, however neither transformation resolveresolves the issue (see residual versus fitted value plot). I have not used coxCox proportional hazards model as the data is not time-to-event data, the data measures force and there are a large number of observations have a reading of zero. I cannot exclude these readings as they are valid.
I have found aan R package that runs Tobit regression (AER). Nevertheless, however this will not accommodate the random effects in the model. I cannot find any R packages that run Weibull mixed effects models (or gamma mixed effects models)...
Does anyone know if there is a package to run these type of models? (or can they suggest any alternative approach).
Many thanks
Etn