I am trying to run a growth curve model with 7 times points of the outcome variables and test the effects of child maltreatment on growth factors. One of the predictors is onset of the maltreatment that I coded 1=infancy, 2=toddlerhood, 3=preschool period, 4=school age period, and 5=later school age period. In the sample, half of children were maltreated and the other half were non-maltreated (control group). If I want to include all children in the model, how should I treat the non-maltreated children for the onset variable? If I assign 0=no maltreatment, it doesn't make sense because 0 would indicate an earlier onset than 1 (infancy). Should I use a set of dummy variables using the non-maltreated group as a reference group? Thanks very much for your help!