The External Validity of Experiments

Abstract

Shortly after publication, Donald T. Campbell and Julian C. Stanley's Experimental and Quasi-Experimental Designs for Research on Teaching (1963) gained the status of a classic exposition of experimentation in education. There have been few attempts to extend this pioneering work, as might be expected of a work so comprehensive in conception and so brilliant in execution. Webb et al. (1966) produced a work similar in purposethat being to identify sources of external invalidity which arise from the reactive effect of measurement. We know of no other