when should outcome variables be measured does bmi need to be measured twice in a longitudinal study should the outcome variable be measured at least twice in a longitudinal study? how much time to measure onset age should bmi be measured twice how many studies should be done on onset bmi should bmi be measured twice in a longitudinal study? should outcome variables be measured twice how often should the outcome variable be measured? what is the expected outcome in a bmi longitudinal study how is bmi measured how many times should the outcome variable be measured in a longitudinal study onset age should be measured twice if longitudinal what should bmi be measured at the same time does bmi matter in longitudinal study how often should the outcome variable be measured should the outcome variable be measured at least twice in a longitudinal study? which condition is associated with onset age of a condition when should a bmi be measured should bmi be used twice?