Research design Faulty or pre-experimental designs True experimental designs
Faulty or pre-experimental designs • One-group after-only design/One-shot case study X O • One-group pretest-posttest design O1 X O2 • Nonequivalent posttest-only design/ Static group comparison X O O
True experimental designs • Characteristics: • Random assignment and matching • Comparison group/control group • As a source of comparison • As a control for rival hypotheses • Generalizability/external validity • Random selection
True experimental designs • After-only or posttest-only control group design: R X O R O • This design may be conducted between participants or within participants. • It may be matched or randomized, thus called matched participants or matched groups design, or randomized participants or randomized groups design.
Randomized groups/participants designs • Simple randomized groups designs R X1 O R X2 O ... R XK O • Factorial randomized groups designs • A x B, eg 2 x 2 or 2 x 3
Within-groups/participants posttest-only designs • A repeated measures design • Problem of sequencing effects • Counterbalancing controls only linear sequencing effects • Within-groups designs control for threats to internal validity, but do not permit their measurement • Used less frequently than between-groups designs
More designs • Mixed model designs • Factorial design based on a mixed model • Factorial design with a control group for A but not for B • Pretest-posttest control group design R O X O R O O • Can be varied through the same combinations as the between-groups designs, but gets very complicated.
Choices in research design • Between-groups or within-groups? • Matching? • How many independent variables? • Simple or factorial designs? • Pretest-posttest or posttest-only? • Control group or comparison group? • How many ways can I randomize?