S W 313 Lecture Notes - Lecture 9: Internal Validity, Random Assignment, Dependent And Independent Variables
Document Summary
Best causal evidence comes from designs with strong internal validity. Experimental designs provide maximum control for threats to internal validity. Assumes that the process of random assignment removes any significant initial differences between experimental and control groups. Assesses amount of pretest-posttest change while checking for testing effects. Participants are divided into groups using procedures based on probability theory. Improves the likelihood that the control group represents what the experimental group would look like had it not been exposed to the experimental stimulus. Ethical considerations require that services be provided to many control groups. Often control groups receive usual care in place of the experimental intervention. Compares experimental intervention to treatment as usual. Control group participants may also be given waitlist priority. Designs that attempt to control for threats to internal validity and thus permit casual inferences but are distinguished from true designs. Two existing groups that appear to be similar are identified or created.
