Chapter 8: Quasi-experimental designs

Quasi-experimental designs

Similar to true experiments but lack either a control group or random assignment to conditions. often used in educational or clinical settings

Threats to internal validity while using quasi-experimental designs

• history

• maturation

• testing

• instrumentation

• regression to the mean

• mortality

One-group pretest-posttest design

An experiment design in which the dependent variable is measured once before the treatment is implemented and once after it is implemented

History

Events outside of the pretest-posttest research design that might have influenced many or all of the participants between the pretest and the posttest

maturation

Participants might have changes between the pretest and the posttest in ways that they were going to anyway because they are growing and learning

Testing

A threat to internal validity that occurs when the measurement of the dependent variable during the pretest affects participants' responses at posttest.

Instrumentation

A potential threat to internal validity when the basic characteristics of the measuring instrument change over the course of the study.

regression to the mean

Refers to the statistical fact that an individual who scores extremely high or extremely low on a variable on one occasion will tend to score less extremely on the next occasion.

Spontaneous remission

The tendency for many medical and psychological problems to improve over time without any form of treatment.

interrupted time-series design

The tendency for many medical and psychological problems to improve over time without any form of treatment.

Nonequivalent groups design

A between-subjects design in which participants have not been randomly assigned to conditions.

posttest only nonequivalent group design

Participants in one group are exposed to a treatment, a nonequivalent group is not exposed to the treatment, and then the two groups are compared.

pretest-posttest nonequivalent groups design

In this design there is a treatment group that is given a pretest, receives a treatment, and then is given a posttest. Then, at the same time there is a nonequivalent control group that is given a pretest, does not receive the treatment, and then is given a posttest.

interrupted time-series design with nonequivalent groups

Involves taking a set of measurements at intervals over a period of time both before and after an intervention of interest in two or more nonequivalent groups.