This book presents a balanced presentation of research methods across disciplinary boundaries—both psychological and sociological, laboratory experiments and survey methods, quantitative and qualitative techniques. It offers a coherent, organizing theme, in this case, that of validity in its various guises-internal, external, inferential statistical, and measurement construct. The organizing theme is validity—the extent to which the researcher's conclusion can be judged credible. Validity is broken down into several components each of which is developed in one or more chapters including construct validity (both measurement and experimental), statistical inference validity, internal validity, and external validity. These validity types are then revisited as appropriate in the treatments of the several basic research approaches—true experimental, quasi-experimental, correlational, and qualitative. Ideal for professionals belonging to various psychological or sociological association or anyone interested in review or updating their current knowledge.