Experimental Research

1. Experimental Research Hanser and Wheeler

2. Principles • Independent Variable • Dependent Variable

3. Control • Random assignment to groups • Setting • Time of day • Therapist • Etc.

4. Generalizability • Random selection/random sample (match population of interest) • Size of sample • Normal distribution • External validity

5. Experimental Design • Way to structure conditions in scientific inquiry • Test hypotheses by controlling certain variables and allowing others to change

6. Hypotheses • Prediction • Null hypothesis • Reject or accept

7. Experimental Designs • Pre-Experimental • True Experimental: Independent Groups • True Experimental: Related Groups • Quasi Experimental

8. Independent Groups • Experimental group – Control group • Random assignment to conditions • Pretest-posttest, posttest only • Three or more groups – multiple levels • Factorial design – interaction effects

9. Related Groups • Subjects act as their own controls • Counteracts individual variety within participant groups • Counterbalancing – order of conditions • Matched pairs – participants matched on age, gender, SES, intelligence, pretest scores, etc.

10. Quasi Experimental • Do not determine cause-effect • Point to relationships that exist • Convenience sample • Ex post facto (after the fact) – researcher does not have control over independent variables because they have already occurred or are not manipulatable

11. Correlational • Researcher examines two or more data sets to note the degree of relationship • Researcher does not determine group membership or arrange/manipulate events; rather she or he studies existing relationships • Used to make predictions

12. Causal-Comparative • Concerned with probable causation • Identify variables or factors and then explain why these factors occurred at a given point in time • Wheeler!