A colleague asked for my help with his thesis project. He performed a
simple experiment. He pretested two classes using the same test. Then he
gave one class a special set of lectures, and gave the other class the
lectures he always uses. Finally, he gave both classes the same posttest.
He wants to see if the special lectures had an effect on the posttest of
the experimental group compared with the posttest of the control group. I
am having trouble coming up with the proper SPSS procecure.
The design is:
Group Observation-1 Stimulus Observation-2
experimental class pretest new-lectures posttest
control class pretest old-lectures posttest
The two groups were not randomly assigned, nor matched along any variable.
However, the groups were not allowed to pre-select themselves into either
class. The class contents were similar in every way except the set of new
lectures. The experimental group did not know that they were being exposed
to new lectures.
I am embarrassed to say that I cannot figure out what SPSS procedure to
perform. The closest I can get is "Independent-Samples T Test". Here, I
used the continuous variables "Pretest" and "Posttest" by "Classes [groups
1,2]". But it doesn't seem to say if the improvement between pretest and
posttest is significantly greater between the two groups. Is that
something I have to do? Or is there a procedure that calculates that for me?
I would be grateful if someone could point me in the right direction. I
will gladly pour over the books if someone would give me a push in the
Thank you very much.