Friday, March 20, 2009

Midterm Blues

Yesterday, just before Harvard's spring break, I gave the midterm for my undergraduate class, and then we spent the afternoon grading it. Hopefully, students don't actually read my blog, so they won't be anxious and disappointed over break. Because on average, they didn't do well.

My midterms are commonly both difficult and long; most students don't finish, and historically the average has been around 65-70%. This year, the average was about 50%.

I'm looking for possible explanations. Here's what I've come up with so far.

1) The test was harder this year. There may be something to that -- some of the new questions I've never used before people did quite poorly on. On the other hand, I also think the class did statistically significantly worse on some of my old stand-by questions than in previous years. This may account for some of the discrepancy -- possibly the top students, who usually can do almost everything on the exam, might have obtained lower scores than usual because of this -- but I don't think it can explain this big a discrepancy.

2) I'm teaching worse this year. There may be something to that -- I am teaching two classes this semester and I do have a 9-month old to cope with -- but I doubt this is an explanation. (Obviously, I'm a bit biased here.) My class doesn't vary significantly from year to year -- same topics, same lecture notes this year as usual. Again, even if I think this had an effect, I don't think it can explain this big a discrepancy. (Similarly, I don't think the issue is the TAs I have this year -- they seem like a really great bunch.)

3) The students are doing less well this year. Unfortunately, here there's some evidence -- the average scores, on the whole, are noticeably lower this year than last year across all assignments so far. That could be variance in TA grading style, and the discrepancy on assignments is nowhere as large as it was with the midterm. But my thought is that perhaps this is an unfortunate flip side to class sizes increasing. The class enrollment has dropped from the mid-80s down to 80 -- but this is still over twice as many people as were taking it last year, and still my second largest class ever. Does larger class size (less self-selection) translate into lower averages?

4) Random chance. Seems unlikely.

5) External considerations outside my scope. Maybe more students are having to deal with other midterms the same day or week this year than usual. Small changes in the class schedule can have big effects this way, since many people have multiple classes in common.

Whatever the reason, it's a situation I'll have to pay some attention to. I may have to adjust the pace and style of the lectures, to better maximize what students learn. But for now, I've got the midterm blues. Yes, professors get them too.


Anonymous said...

New difficult questions might hurt results on older questions just because of the time management issue.

But I think it's class size.

Anonymous said...

4) Random chance. Seems unlikely.
How unlikely is it, exactly?

Anonymous said...

Hmm, could be entirely coincidental (perhaps we should ask Persi Diaconis?), but my husband and I have noticed the same thing this year in our classes (in a different state from yours, and in different disciplines, and in different types of institutions; one of us teaches finance in an MBA program at a flagship public university and the other teaches economics at a very good liberal arts college) Both of us have taught our respective courses many times before, and something seems "off" this year.

Economic worries are weighing heavily on many of our students' families--perhaps this could be a factor making it hard to concentrate.

Panos Ipeirotis said...

I observed that whenever I teach smaller classes, the average grades are higher. So, my hypothesis is that class size plays a significant role.

But why? I believe that larger classes interact with the quality of learning: in small classes, a comparatively higher fraction of students can ask questions and participate. As the class size grows, students do not have the same level of access to the professor. Furthermore, big set of peers discourages students from asking questions being "afraid" of peer judgment.

There is a reason that, in K12 education, classes are not bigger than 30-35 students. Learning abilities do not change suddenly when someone graduates from high school.

This is a link that I found after some quick Google search:

Anonymous said...

Peer judgment is a huge factor in large classes. Did you see a drop in questions during the classes?

Often one student will serve as the canary in the coalmine by asking the question that everyone wants to ask but are too afraid to. (i.e. you said something horribly confusing and everyone clamours for some clarity).

This works fine in small classes as the canary chirps up, but large classes tend to suffocate canaries. (If there are 3 canaries, they may all standoff waiting for each other, as they don't want to be perceived as the dolt in the class.)

It sounds so trivial, but the "interested student" in a small class quickly becomes perceived as the "suck up shmuck" in the large classes. Finally, large classes become more structured just to maintain some level of organization, and asking a question in the middle breaks that structure much more than in a small, more fluid classroom.

I would very carefully consider large class effects. More data!

Matt Welsh said...

Remember a lot of students making be taking your class to satisfy the secondary concentration requirement, which we did not have before - hence, more students are in the class that are not CS majors (and may be less prepared).

Anonymous said...

Irrespective of the midterm scores, most students in Harvard get mostly A grades in their courses (according to many claims) - unlike say Princeton :-)

Michael Mitzenmacher said...

I think many of the comments have possibly valid points: externalities (the economy! hadn't thought of that) may be playing a role, class size -- either because it's leading to different class dynamics, or because it means less prepared students -- certainly seems to be related in some way. Too bad this isn't a conveniently repeatable experiment.

It's not true that most students get A grades in Harvard CS courses, from my understanding... I can't speak for other courses. :)

Anonymous said...

A lot of students do read your blog.

Anyways, scheduling was probably part of it. The midterm this year was on Housing Day - you probably noticed that campus was in total chaos - and there were several other midterms that day too.

David said...

At 31 [four years ago], I started my master's degree. I was well into the career phase. It's interesting to me, from a purely professional point of view, how many kids think that just getting to the end is the accomplishment.

I don't buy the, "The day of XYZ arguments," because by the time that you get to exam day, you should have read, reviewed, and understood the material thoroughly. The exam should be a practical exercise, not so much a challenge.

Anonymous said...

I'm a newcomer to your blog and have enjoyed it thus far. When I was a student, many years ago, I struggled with various subjects, similar to the ones you teach now.
For example, here is some commentary of mine on why engineering is hard. If you have a chance, take a look, read some of the responses, and let me know what you think.

Anonymous said...

It was housing night!