title: The law of attrition revisited.
authors.forename: Helen
authors.initials: H
authors.lastname: Christensen
authors.forename: Andrew
authors.initials: A
authors.lastname: Mackinnon
mesh_terms: D006302:Health Services Research / Q000706:statistics & numerical data*; D006801:Humans; D020407:Internet / Q000706:statistics & numerical data*; D008491:Medical Informatics Applications; D010352:Patient Dropouts