Chapter 8

Experience carefully exploited:

Quasi-experimental research designs

Why Quasi-Experiments?

• Maximize internal and external validity

• When random assignment can’t be done

• When random assignment shouldn’t be done

Kinds of Quasi-Experiments

• Person-by-treatment quasi-experiments

• Natural experiments• Nature and treatment designs

– Natural groups with experimental treatment

– Nature-by-treatment studies

Comparability and Patching

• Comparable and non-overlapping groups

• Patched-up designs:– One group, pretest-posttest design– Posttest-only with nonequivalent groups– Pretest-posttest with nonequivalent groups

• Time-series designs• Internal analyses

When True Experiments and Quasi-Experiments Collide

• Consistencies and inconsistencies in the results of true experiments compared to quasi-experiments

Key Terms from Chapter 8• Person-by-treatment

quasi-experiment• Prescreening• Extreme groups• Median split• Natural experiments• Natural groups with

experimental treatment

• Comparable and non-overlapping groups

• Patched-up design• Patching• One-group design• One-group pretest-

posttest design• Posttest-only design

with non-equivalent groups

Key Terms from Chapter 8• Pretest-posttest

with non-equivalent groups

• Time-series design

• Internal analysis• Name-letter effect