I would like to hear from experts what is the difference between Randomized Control Trials and True experimental designs ( Post test-only design with control group/Solomon four-group design). I understand both these designs have manipulation, control, and randomization. What type of studies can be done using RCT? In the hierarchy of evidence, where does the Post-test only control design (one of the true experimental designs) come from?
An easy way to look at this is a "true experimental design" is a car and a "Randomized Control Trials" is a Toyota. That is, a true experimental design is a broader term that covers a type of designs. A Randomized Control Trial is a specific type of true experimental design.
Thank you, Dr. James E. McLean. Your example is interesting, simple, and to the point and it clarifies my query.
I see randomized control trials as similar to true experiment design. There are two types of experimental designs,
1) quasi experimental design - selection of subjects into groups is not done via randomization
2) true experimental design - selection of subjects into groups is done via randomization. This is what I think is equivalent to randomized control trials.
True experiment has its own variants ie
1) pretest - posttest control group
2) posttest only
3) Solomon 4
Quasi experimental design has its own variants ie ...
All RCT will be true experimental but all experimental designs may not be RCTs. I mean the extend of control applied in a RCT would be much tighter than an experimental design where it might be able to explain the cause and effect relationship of a phenomenon under study. Where as all experimental design may not explain a cause and effect relationship. ( I m not an expert but sharing my understanding here)
1. In my opinion, randomization is the main criteria for RCT.
2. Whenever the pre-test data cannot be collected, then it will be categorized under post-test only experimental design.
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