Hi readers, I'm new to the R package and have a question about handling missing data in R. I have a dataset from a longitudinal study where we are are testing a series of models, some in which lagged variables are used to predict an outcome and others in which concurrent variables are used. Due to the nature of our experiment, every participant (or case) has missing data for the first observation for all of the lagged variables. My question is how does R handle missing data of this nature. My concern is that if I use listwise deletion, I would end up deleting all the participants in the dataset. However, I don't want to omit the first observation from analysis either. Is it possible to simply omit the first observation when the lagged variables are in the model (that is, when there is missing data from the first observation), but include the first observation when there are not lagged variables in the model (that is, when there is no missing data)? Thanks, Tim [[alternative HTML version deleted]]