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Experimental Designs.

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Presentation on theme: "Experimental Designs."— Presentation transcript:

1 Experimental Designs

2 Campbell & Stanley’s (1963) three general types of experimental designs
Pre-experiments Quasi-experiments Full or true experiments

3 Key concepts Random assignment: assigning participants to the various conditions in an experiment to achieve equivalent groups for comparison purposes. Treatment condition: administering the experimental manipulation Control condition: no experimental manipulation or an alternative, benign manipulation Pretest: measurement of the dependent variable(s) prior to exposure to a treatment or control condition Posttest: measurement of the dependent variable(s) following the treatment or control conditions.

4 notation for experimental designs
R = random assignment 01 = pre-test (measurement) 02 = post-test (measurement) X1 = treatment, stimulus condition, or manipulation X0 = control group (no treatment)

one-shot case study: A group (usually intact) is administered a treatment and then measured or observed. No attempt is made to randomly assign subjects to condition, nor does the design provide for any additional groups as comparisons. (no random assignment) X1 O1 one group, pre-test, post test design (no random assignment) O1 X O2 static group comparison: only one of two intact groups is given the experimental treatment. At the end of the treatment, both groups are observed or measured to see if there is a difference between them as a result of the treatment. (no random assignment) X1 01 X0 01 PRE-EXPERIMENTAL DESIGNS

6 Quasi-experimental designs
Pre-test, post-test, quasi-equivalent groups design (no random assignment) X O2 O2 Times-Series design

pre-test/post-test equivalent groups design R 01 X O2 01 O2 post-test only equivalent groups design R T O1 O1 Solomon four-group design R 01 X O O2 X O2 O2 FULL EXPERIMENTAL DESIGNS

8 true/full experimental designs
Solomon Four Group design: attempts to control for the possible "sensitizing" effects of the pre-test or measurement by adding two groups who have not been a part of the pre-test or pre-measurement process. R 01 X1 O O2 X1 O2 O2

9 Factorial designs (may be full or quasi-experimental)
Advantage: Allows the researcher to uncover interaction effects 2 X 2 design Two independent variables Two levels/values per variable Four conditions being compared 3 X 2 X 2 design Three independent variables Three levels/values for one independent variable, two levels/values for the other two independent variables Twelve conditions being compared

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