PSYB01H3 Lecture Notes - Repeated Measures Design, Confounding, Internal Validity
Document Summary
In the experimental method, all extraneous variables are controlled. When the results of an experiment can confidently be attributed to the effect of the independent variable, the experimenter is said to have internal validity. The experimental method involves control over extraneous variables, through either keeping such variables constant (experimental control) or using randomization to make sure that any extraneous variables will affect both groups equally. A researcher using a posttest-only design must obtain two equivalent group of participants, introduce the independent variable, and measure the effect of the independent variable on the dependent variable. Finally, the effect of the independent variable is measured; the same measurement procedure is used for both groups, so that comparison of the two groups is possible. Because the groups were equivalent to begin with and there were no confounding variables, any difference between the groups on the dependent variable must be attributed to the effect of the independent variable.
