as “studies that do not involve the application of treatments via random assignment of subjects.  They are also called observational studies.”

This reader thought the concepts of observational study and quasi-experiment should be disentangled, i.e.

• Experiment:  Randomization + treatment applied
• Observational Study:  No randomization, no treatment
• Quasi-experiment:  Comparison groups with no randomization, or one group with multiple pre/post measures, + treatment applied

This is not my field, but it makes sense so I thought I’d pass it along.