Experimental, Factorial, and Repeated Measures Designs

1. Experimental, Factorial, and Repeated Measures Designs P291 Research Methods November 25-27, 2013

2. Well designed experiments have: • Research hypotheses with specifically predicted causal effects • At least 2 levels of one IV • Random assignment of participants • Procedure for empirically testing the hypothesized causal relationship • Specific controls to reduce threats to internal validity

3. Random Sampling • Procedure for selecting participants in which each participant has an equal chance of being selected and the selection of any one participant does not affect the probability of selecting another • Random number generator • Coin flipping • Rolling a die

4. Conditions • Experimental Conditions • At least 1 IV with at least 2 levels • Manipulation • Control Conditions • Baseline or non-manipulated level of IV • Manipulation check

5. Between Subjects Design (Post-Test only Design) A psychologist wanted to examine the effects of diet on learning in rats. Newborn rats were randomly assigned to one of two diets: standard Purina Rat Chow or a supplemented diet where vitamins and minerals were added to the Rat Chow. After 6months, each rat was tested in the Radial Arm Task, and the researcher recorded the number of errors each animal made before it solved the problem. What is the IV? What is the DV? How do you know this is a Post-test only design?

6. Randomized Pre Test – Post Test Design A psychologist wanted to examine the effects of environmental enrichment on learning in rats. Rats were tested in the Radial Arm Task following quarantine. The rats were then randomly assigned to one of two conditions: a standard home environment or an enriched junglegym environment. After 6 months, each rat was retested in the Radial Arm Task, and the researcher recorded the number of errors each animal made before it solved the problem. What is the IV? What is the DV? How do you know this is a Pre/Post Test design?

7. Factorial Designs • Designs employing more than one independent variable and thus allowing researchers to identify interactive effects among independent variables • Experiments with Quasi-independent variables are necessarily FD • FD are described by the number of levels of each IV e.g. 2 x 2 x 3 • How many IVs are there in this study? • How many levels of each? • How many groups would there be in total?

10. Repeated Measures Designs • Any design in which participants are tested more than once • Ps may be tested repeatedly at different levels of IV or in same condition repeatedly (i.e. trials) • The DV is the same across all measures, regardless of type of RM design

11. RM as Different levels of IV Researchers wanted to investigate the effect of different types of interventions on stress levels in Participants. Participants were involved in a 6 week study where they were guided in three different interventions. The orders were counterbalanced with a 2 week break between sessions.

12. RM as Effect of Trials Alternative guided exercise classes are becoming more popular forms of exercise however many people attend only a single class before deciding whether or not to regularly attend the class. For classes with elaborate routine based classes (e.g. Zumba), instructors were interested in changes to the number of calories burned during a session as attendees became more familiar with the routines. Participants were asked to wear heart rate monitors throughout the class to determine the number of calories burned.