In a purely statistical context, random assignment in a trial meets all the required assumptions and as such it is an exclusion restriction by definition.
KC carried out the random assignment, allocation, and trial registration and drafted the manuscript.
Because this was a cross-sectional study, we could not imply causation from these results; only random assignment within a trial could determine whether skipping breakfast reduces PA.
With the potential for selection bias among the patients who decide to cross over, the benefits of random assignment erode and the trial becomes a hybrid of a randomized trial and observational study.
In addition, the following factors used to stratify randomization were included in each model: glycemia treatment group, assignment to the blood pressure or lipid control trial, random assignment to the intensive blood pressure treatment, randomization to fenofibrate, clinical center network, and prior history of cardiovascular disease.
Reasons for attrition may differ for randomized trials, e.g. random assignment to an unwanted treatment group, and the process of randomization and the types of interventions, which, make it difficult to extrapolate the effectiveness of certain retention methods to cohort studies.
Design: An experimental, within-subject design with two-trial random assignment was used.
Controlled, multicentre, community intervention trial, with random assignment by PHCT group.
The sampling strategy implemented in Yemen was a randomised controlled trial with random assignment of matched pairs of schools.
