Quasi Experimental Design

This document will help you in developing your concept about Quasi experimental design

Cohort design- A design consisting of a longitudinal study of several groups.
Control group –That group which does not receive the treatment in an experiment. Counterbalancing -A technique used to vary systematically the order of conditions in an experiment so that the distribution of the effects of the time of testing (that is, practice
and fatigue) is not confounded with the conditions of the experiment.
Experimental group -That group which receives the treatment in an experiment.
Experimental mortality– Experimental Mortality refers to the loss of subjects from experimental conditions for whatever reason. Animal subjects may die or become sick during the course of an experiment and, as a result, may have to be dropped from the experiment. Human subjects may decide to drop out before an experiment is completed. The longer is the period of the participation or the greater are the demands placed on the subject, the more likely is the possibility of experimental mortality.
External validity: Extent to which the results of a study or a research can be generalized to different populations or settings.
Extraneous variables which may potentially influence the results of a study but are not the variables whose effects are to be studied by the experimenter.
Internal validity: The extent to which differences in dependant variables can be clearly attributed to an effect of independent variables as opposed to the effect of extraneous variables. In other words, the extent to which any experiment or research study is methodologically sound or free from confounding.
Longitudinal design- A design in which individuals are studied over time, and measurements are taken on the individuals at various intervals.
Pre-experimental designs -Designs that incorporate the least basic elements of an experimental design. They do not provide a control group or an equivalent of a control group and are hence generally weak in controlling for internal validity. Also sometimes referred to as ‘non designs’.
Quasi-experimental design- A research design that resembles a true experimental design but subjects are not randomly assigned to treatments nor are the treatments randomly assigned to the group; such a design is basically an attempt to stimulate the true experiment whose criteria are only partially met, that is, control over manipulation of independent variables is somehow achieved but control over assignment of subjects into equivalent groups is not achieved.
True experimental designs Designs- that are the strongest in terms of controlling for internal and external validity, particularly internal validity. In these designs the control and experimental groups are formed and their equivalence is established through randomization.