Experimental Research

Internal Validity, the strength of experimental research is due to its ability to link cause and effect through treatment manipulation, while controlling for spurious effect of extraneous variables. ≈≈≈≈≈≈≈≈≈

Laboratory Experiments, an experiment conducted under highly controlled conditions making accurate measurements possible.

External Validity, the validity of applying the conclusions of a scientific study outside the context of that study.

Field Experiments, experiments carried out outside of laboratory settings.

Basic Concepts

Treatment Groups, subjects that are administered one or more stimulus.

Control Group, subjects are not given a stimulus.

Treatment Manipulation, helps control for the "cause" in cause-effect relationships.

Pretest measures, measurements conducted before the treatment is administered.

Posttest measures, measurements conducted after the treatment.

Threat to internal validity: history threat, maturation threat, testing threat, instrumental threat, mortality threat, and regression threat.

Two-Group Experimental Designs

Pretest-posttest control group design, subjects are randomly assigned to treatment and control groups, subjected to an initial measurement of the dependent variables of interest and the dependent variables measured again.

Posttest-only control group design, a simpler version of the pretest-post test design where pretest measurements are immured.

Covariance designs, measures of dependent variables may be influenced by extraneous variables, which are variables that are not of central interest to an experimental study.

Designs

Factorial designs, Two-group designs are inadequate if your research requires manipulation of two or more independent variables. In a factorial a main effect is said to exist if the dependent variable shows a significant difference between multiple levels of one factor, at all levels of other factors.

Hybrid Experimental Design, randomized block design (variation of the posttest-only or pretest-posttest control group design where the subject population can be grouped into relatively homogenous subgroups within which the experiment is replicated. Solomon four-group design, the sample is divided into two treatment groups and two control groups.

Switched replication design, two-group design implemented in two phases with three waves of measurement.

Quasi-Experimental Design

Nonequivalent groups design, quasi-equivalent version of pretest-posttest control group.

Non-equivalent switched replication design, the quasi-experimental version of switched replication design.

Regression-discontinuity design, a non-equivalent pretest-posttest design where subjects are assigned to treatment or control group based on cutoff score on a preprogram measure.

Proxy pretest design, similar to the NEGD design, the pretest score is collected after the treatment is administered.

Separate pretest-posttest sample design, useful if it is not possible to collect pretest and posttest data from the same subjects for some reason.

Nonequivalent dependent variables is a single-group pre-post quasi-experimental design with two outcome measures, where one measure is theoretically expected to be influenced by the treatment and the other measure is not.