PY 355 Lecture Notes - Lecture 15: Interrupted Time Series, Time Series, Internal Validity

• School: University of Alabama
• Department: Psychology
• Course: PY 355
• Professor: Craig Walter Cummings

Document Summary

Potential threat to internal validity - cannot be sure that the groups were the same before the treatment: nonequivalent groups pretest-posttest design: both groups are measured before and after the quasi-independent variable. Potential threat to internal validity - local history effect local history effect: something else may happen to one group that does not happen to the other group (selection-by-history interaction) An interrupted time series design that includes a nonequivalent control group that does not receive the quasi-independent variable. Helps rule out certain history effects: comparative time series design. Examines two or more variables over time in order to understand how changes in one variable are related to changes in another variable. Provides indirect evidence that the change in one variable may be causing the change in the other variable. Difficult to obtain participants who agree to be in a study over a long period of time.