No, not because of this, although it can get rough.

I teach the third course in the first year PhD micro sequence at Northwestern and I also teach my intermediate micro course in the Spring.  I am just finishing up teaching this week and my students will soon be writing their evaluations of me.  They will grade me on a scale of 1 to 6.

Because I am the third and last teacher they will evaluate this year, I face some additional risk that my predecessors did not.  Back in the fall, when they evaluated their first teacher they had only one data point with which to estimate the distribution of teaching ability in the Northwestern economics faculty. An outstanding performance would lead them to revise upward their beliefs and a poor performance would revise their beliefs downward.

As a result, when the students sit down to evaluate their fall professor, even a very good performance will earn at most a 5 because the students, now anticipating higher average performance in the winter and spring, will be inclined to hold that 6 in reserve for the best.  Likewise, very bad performances will have their ratings buoyed by the student’s desire to save the 1 for the worst.

When Spring comes, there is nothing more to learn.  By now they know the distribution and the only thing left to do is to rank their Spring professor relative to those who came earlier.  If he is best he gets a 6, if not he gets at most a 4.  His rating is a mean-preserving spread of the previous ratings.

There is a general principle at work here.  The older you get the more you know about your opportunity costs, the more decisively you act in response to unanticipated opportunities.  (There is a countervailing force which I believe on net makes us more conservative when we get older, but that is the topic of a later post.)

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