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Quasi-experimental study

A semi-experimental study or quasi-experimental study has the properties of both experimental and non-experimental studies; part of the study may be non-experimental and the other part experimental.
Types of experimental design

There are many types of experimental design as

• 
  after-only experimental design;
  
• 
  before-and-after experimental design;
  
• 
  control group design;
  
• 
  double-control design;
  
• 
  comparative design;
  
• 
  ‘matched control’ experimental design;
  
• 
  placebo design
  

The after-only experimental design

In this design the researcher knows that a population is being, or has been, exposed to an intervention and wishes to study its impact on the population. The information on baseline – pre-test or before observation, is usually ‘constructed’ on the basis of respondents’ recall of the situation, or from information available in existing records – secondary sources. The change in the dependent variable is measured by the difference between the ‘before’ – baseline and ‘after’ data sets.