Types of Designs
There is a random assignment of subjects to different interventions or to an intervention and a control condition.
Randomized Experimental
Uncontrolled or unplanned events that occur during the study.
Extraneous Events
An experiment in which there is no random assignment of subjects.
Quasi-experimental
Inherent differences among comparison groups that influence results
Selection
This type of experiment there is no random assignment and in some cases no pretest or comparison group.
Pre-experimental
Natural changes in subject because they get older, stronger tired, etc
Maturation
Systematic loss of subject during the study
Subject Attrition