PSYC 2230 Lecture Notes - Lecture 10: Interrupted Time Series, Random Assignment, Internal Validity
Document Summary
But lack the degree of control found in true experiments. Generally occur when the iv involves: subject variables (e. g personality type), an environmental event (e. g. hurricanes or having a particular classroom teacher), the passage of time. Hedrick, bickman and rog (1993) a quasi-experimental design is not the method of choice, but rather a fallback strategy . Cannot infer cause and effect, but well designed quasi-experiments enable you to demonstrate that rival interpretations are rendered unlikely. Post test only nonequivalent control group design (aka static group comparison) Because there is no random assignment to groups, confounding variables may explain any. No randomly assigned therefore we do not know if the two groups are equivalent at the difference observed. beginning. Most common threat to internal validity of this type of design is selection. This is because the two groups may be different on a number of variables such as age gender iq but we do not know.
