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

10.0 Introduction 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 10.1Fig 10.1  Back to Chapter Contents

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

10.1 Research Designs with Threat to Internal Validity -1 One-Group Posttest-Only Design TreatmentResponse Fig 10.2 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  Back to Chapter Contents

10.1 Research Designs with Threat to Internal Validity -2 One-Group Pretest-Posttest Design PretestTreatmentPosttest Fig 10.3 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  Back to Chapter Contents

10.1 Research Designs with Threat to Internal Validity -3(end) Nonequivalent Posttest-Only Design TreatmentPosttest Fig 10.4 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  Back to Chapter Contents

10.2 Requirements of Experimental Research Designs 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  Back to Chapter Contents

10.3 Pretesting Participants 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  Back to Chapter Contents

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

10.4 Experimental Research Designs -1 Posttest-Only Design Fig 10.5 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 Fig Within-participants — same participants respond in the various treatment conditions  Back to Chapter Contents

10.4 Experimental Research Designs -2 Posttest-Only Design: Between-participants Simple-Randomized Participants Design Fig 10.8 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  Back to Chapter Contents

10.4 Experimental Research Designs -3 Components of a Factorial Design Fig 10.9 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 10.1 Fig Tab 10.1Fig  Back to Chapter Contents

10.4 Experimental Research Designs -4 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  Back to Chapter Contents

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

10.4 Experimental Research Designs -6 Factorial Design based on a Mixed Model Fig Fig 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  Back to Chapter Contents

10.4 Experimental Research Designs -7(end) Pretest-Posttest Design Fig Fig 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  Back to Chapter Contents

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