title: Difference in difference: simple tool, accurate results, causal effects.
authors.affiliation: Health Division, Impaq International.
authors.forename: Guido
authors.initials: G
authors.lastname: Cataife
authors.affiliation: Department of Laboratory Medicine, University of Washington, Seattle, Washington.
authors.forename: Monica B
authors.initials: MB
authors.lastname: Pagano
mesh_terms: D001803:Blood Transfusion; D006801:Humans; D015233:Models, Statistical