Gus Gassmann <[EMAIL PROTECTED]> wrote in sci.stat.edu:
>Stan Brown wrote:
>> Another instructor and I gave the same exam to our sections of a
>> course. Here's a summary of the results:
>> Section A: n=20, mean=56.1, median=52.5, standard dev=20.1
>> Section B: n=23 mean=73.0, median=70.0, standard dev=21.6
>>
>> So let me pose my question: given the two sets of results
>> shown earlier, _is_ there a valid statistical method to say whether
>> one class really is learning the subject better than the other, and
>> by how much?
>
>Before you jump out of a window, you should ask yourself if there
>is any reason to suspect that the samples should be homogeneous
>(assuming equal learning). Remember that the students are often
>self-selected into the sections, and the reasons for selecting one
>section over the other may well be correlated with learning styles
>and/or scholastic achievements.
You assume that it was my section that performed worse! (That's
true, but I carefully avoided saying so.)
Section A (mine) meets at 8 am, Section B at 2 pm. Not only does the
time of day quite possibly have an effect, but since most people
prefer not to have 8 am classes we can infer that it's likely many
of the students in Section A waited until relatively late to
register, which in turns suggests they were less highly motivated
for the class.
The dean has suggested the same self-selection hypothesis you
mention. Another possible explanation, which I was unaware of when I
posted, is that the instructor for section B held a review session
for the half hour just before the exam.
So no, I'm not jumping out of any windows. (I did hand out a lot of
referrals to the tutoring center.) Mostly I was curious about
whether the apparent difference was a real one (as Jerry Dallal has
confirmed it is). But as you suggest, we may have two different
populations here.
--
Stan Brown, Oak Road Systems, Cortland County, New York, USA
http://oakroadsystems.com
My reply address is correct as is. The courtesy of providing a correct
reply address is more important to me than time spent deleting spam.
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