What is the major characteristic of a retrospective,or ex post facto,study?

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The major characteristic of a retrospective, or ex post facto, study is that the dependent variable has already been affected by the independent variable. This is because the study is conducted after the exposure has occurred, and the researcher cannot manipulate or control the independent variable. Informed consent is still necessary, and there is no opportunity for manipulation of the independent variable. Multiple measurements of the dependent variable may be taken, but this is not a defining characteristic of a retrospective study.

What Is the Major Characteristic of a Retrospective,or Ex Post