2 Campbell & Stanley’s (1963) three general types of experimental designs Pre-experimentsQuasi-experimentsFull or true experiments
3 Key conceptsRandom assignment: assigning participants to the various conditions in an experiment to achieve equivalent groups for comparison purposes.Treatment condition: administering the experimental manipulationControl condition: no experimental manipulation or an alternative, benign manipulationPretest: measurement of the dependent variable(s) prior to exposure to a treatment or control conditionPosttest: measurement of the dependent variable(s) following the treatment or control conditions.
4 notation for experimental designs R = random assignmentN = no random assignment01 = pre-test (measurement)02 = post-test (measurement)X1 = treatment, stimulus condition, or manipulationX0 = control group (no treatment)
5 Pre-experimental designs 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.N X1 O1one group, pre-test, post test design N O1 X O2static 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.X1 01Nintact groups, no pretestNX001
6 Quasi-experimental designs Pre-test, post-test, quasi-equivalent groups designN X O2N O2Times-Series designN
7 Full Experimental Designs pre-test/post-test equivalent groups design R 01 X1 O201 O2post-test only equivalent groups design R X1 O1O1Solomon four-group design R 01 X1 O O2X1 O2O2a.k.a. two-group posttest only design
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 O2X1 O2O2
9 Factorial designs (may be full or quasi-experimental) Advantage: Allows the researcher to uncover interaction effects2 X 2 designTwo independent variablesTwo levels/values per variableFour conditions being compared3 X 2 X 2 designThree independent variablesThree levels/values for one independent variable, two levels/values for the other two independent variablesTwelve conditions being compared