Experimental & Ex-post Facto Research

In the last session I provided a brief overview of the experimental and ex-post facto designs. Basically here is how they differ.

Experimental

Research question: Are songs effective to teach listening comprehension?

Design:

You draw the sample randomly from the population.
Then you assign the sample into an experimental and control groups also randomly.
You give a treatment to the experimental group, but not to the control one.


Ex-post Facto

Research question: Does learning English in elementary school affect the university students’ speaking ability?

Design:

There is no randomization here.
You select the subjects on the basis of a certain existing condition.
You do not give treatment to any group because:
1. the “treatment” already happened in the past and you can no longer do anything about it, or
2. it is unethical to give a treatment to the ex-post facto group.

We will discuss more about the above designs near the end of this semester.