Abstract Clinic-based cohort studies enroll patients on first being admitted to the clinic, and follow them as part of usual care, with interest being in the marginal mean of the outcome process. As the required frequency of follow-up varies among patients, these studies often feature irregular...

We describe a means of rejecting a null hypothesis concerning observed, but not deliberately manipulated, variables of the form H0: A -/- B in favor of an alternative hypothesis HA: A -- B, even given the possibility of causally related unobserved variables. Rejection of such an H0 relies on the...