Experimental Research Design ♣

1. Experimental Research Design ♣ Chapter 10 Back to Brief Contents • Introduction  • Research Designs with Threats to Internal Validity • Requirements of Experimental Research Designs  • Pretesting Participants  • Experimental Research Designs • Choice of a Research Design

2. 10.0 Introduction Back to Chapter Contents • Research Design—the outline, plan, or strategy used to answer the research question • Purpose of research design • Specify: how to collect data, analyze data • Control for unwanted variation • Suggest the conclusions that can be drawn (e.g.) Fig 10.1

3. 10.1 Research Designs with Threat to Internal Validity -0 Back to Chapter Contents • One-Group Posttest-Only Design • One-Group Pretest-Posttest Design • Nonequivalent Posttest-Only Design

4. 10.1 Research Designs with Threat to Internal Validity -1 Back to Chapter Contents • One-Group Posttest-Only Design Treatment Response Fig 10.2 X Y • Rarely useful because no pretest or control group • Almost all threats to internal validity apply • Is useful only when specific background information exists on the DV Threat

5. 10.1 Research Designs with Threat to Internal Validity -2 Back to Chapter Contents • One-Group Pretest-Posttest Design Pretest Treatment Posttest Fig 10.3 Y X Y • Most threats to internal validity exist • To infer causality must identify and demonstrate that internal validity threats do not exist Threat

6. 10.1 Research Designs with Threat to Internal Validity -3(end) Back to Chapter Contents • Nonequivalent Posttest-Only Design Treatment Posttest Fig 10.4 Exper. Gp. X Y Control Gp. Y • No assurance of equality of groups because they were not randomly assigned • May confound selection with treatment effect Threat

7. 10.2 Requirements of Experimental Research Designs Back to Chapter Contents • Answer the research question or test the hypothesis • Control for the effect of extraneous variables • With control techniques • With a control group—group that does not get the IV or gets some standard value • Serves as source of comparison to experimental group • Controls for rival hypothesis • Should allow generalizability of the results

8. 10.3 Pretesting Participants Back to Chapter Contents • To increase sensitivity through matching • To test for a ceiling effect • To test for initial position • To insure initial comparability • To obtain evidence of change • Difficulties: sensitize

9. 10.4 Experimental Research Designs -0 Back to Chapter Contents • Posttest-Only Design • Between-Participants Posttest-Only Design • Within-Participants Posttest-Only Design • Combing Between- and Within-Participants Designs • Pretest-Posttest Design

10. 10.4 Experimental Research Designs -1 Back to Chapter Contents Posttest-Only Design Fig 10.5 • Between-participants—different participants randomly assigned to the various treatment conditions • Can also match participants prior to random assignment to insure equivalence on the matched variable • (e.g.) Two levels:Fig 10.610.7 • Within-participants—same participants respond in the various treatment conditions

11. 10.4 Experimental Research Designs -2 Back to Chapter Contents Posttest-Only Design: Between-participants • Simple-Randomized Participants Design Fig 10.8 • Used with more than 2 levels of 1 IV • Participants randomly assigned to group • Factorial Design • Used to test • The effect of more than one IV • The interaction of several IV’s • Participants randomly assigned to groups

12. 10.4 Experimental Research Designs -3 Back to Chapter Contents Components of a Factorial Design Fig 10.9 • Cell—a treatment combination of two or more IV’s • Main effect—the effect of one IV • Interaction effect—when the effect of one IV depends on the level of another IV Tab 10.1Fig 10.1010.1110.12

13. 10.4 Experimental Research Designs -4 Back to Chapter Contents Factorial Design • Difficulties with factorial designs • Increase in the number of research participants • Difficulty in manipulating more than one IV • Difficulty in interpreting higher-order interactions. • Advantages of factorial designs • Can manipulate more than one IV • Can control potential extraneous variable by building it into the design • Provides greater precision when adding more than one IV • Can test the effect of interactions

14. 10.4 Experimental Research Designs -5 Back to Chapter Contents Within-Participants Design Fig 10.13 • Advantages of within-participants design • Equivalence of research participants • Requires fewer participants than between-participants design • Disadvantage of within-participants design • Sequencing effect

15. 10.4 Experimental Research Designs -6 Back to Chapter Contents Factorial Design based on a Mixed Model Fig 10.14 • Characteristic is that it has a between and a within component • At least one IV requires different participants for each level of variation • At least one IV requires the same participants in each level of variation • Participants randomly assigned to between component

16. 10.4 Experimental Research Designs -7(end) Back to Chapter Contents Pretest-Posttest Design Fig 10.15 Primary unique characteristic is that it includes a pretest in addition to a posttest Pre- test Treatment Post-test Exper. Gp Y X Y Control Gp Y Y

17. 10.5 Choice of a Research Design Back to Chapter Contents • Research Question • Control • Between- versus Within-Participants Design • Control rival hypotheses (internal validity) • Most sensitive test