title: Sampling and external validity.
authors.affiliation: Colorado State University, Fort Collins, USA.
authors.forename: G A
authors.initials: GA
authors.lastname: Morgan
authors.forename: R J
authors.initials: RJ
authors.lastname: Harmon
mesh_terms: D003625:Data Collection / Q000379:methods*; D006801:Humans; D011897:Random Allocation; D015203:Reproducibility of Results; D018401:Sample Size