title: The internal validity of efficacy studies: design and statistical power in studies of language therapy for aphasics.
abstract: In this study the internal validity of efficacy studies of language therapy for aphasic patients is discussed. The lack of sufficient internal validity is demonstrated with respect to research designs used in these studies and the statistical power of their statistical significance tests. The internal validity problems are viewed as the major cause of the conflicting conclusions in the efficacy studies in the past three decades.
authors.affiliation: Institute for General Linguistics, University of Amsterdam, The Netherlands.
authors.forename: R
authors.initials: R
authors.lastname: Schoonen
mesh_terms: D001037:Aphasia / Q000628:therapy*; D006801:Humans; D007808:Language Therapy / Q000706:statistics & numerical data*; D015233:Models, Statistical; D017063:Outcome Assessment, Health Care / Q000706:statistics & numerical data; D015203:Reproducibility of Results; D012107:Research Design