PSYCH 241 Lecture Notes - Lecture 4: Causal Inference, Convergent Validity, Internal Validity
18 Oct 2016
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Internal validity the degree to which differences in performance (the dependent variable) can be attributed unambiguously to an effect of the independent variable. The conditions necessary for internal validity: time-order relationship, co-variation, elimination of other plausible alternatives. * to test hypotheses about the cause of phenomena : hypothesis may be based on descriptive or predictive research. True experiment is best available method for establishing cause and effect (drawing causal inference: has to be done correctly assign, manipulate, control. Multimethod approach very powerful convergent validity. If numerous experiments lead to same conclusions strengthened: replicate, replicate and extent, within & across labs confidence. Three key steps: random assignment of subjects, manipulation of iv dv, control of external factors. Control is essential, and is achieved through: manipulation of iv, holding other variables constant, & balancing. Manipulate iv to observe effect on dv. Appropriate control allows researcher to eliminate plausible alternatives and make a causal inference the iv caused the change in the dv.
