Dear All, What is the minimal group size for level sufficient to use "sts test var, trend"? Specifically, having many levels in var, say, var = 1,2,3,..15 I want to check the trend for survivor functions for 1, 2, ,,,15 but not sure what is the minimal groups size required for each level var = 1, 2, 3, ....15. I know we can use this also for, say, var = 1, 1.5, 2.5 , .... but can't find any suggested minimal group size for each var value to make sure I can use this "sts test var, trend" test. Stata calculates this even having one observation for some levels (so it looks I can do kind of univariate analysis for continous variable, but one-observation survivor function used in testing the trend for all the levels rather doesn't make sense). If using "sts test var, trend strata(dummy)", what would be then minimal group required for all levels in dummy==0 and in dummy==1. Many Thanks.