The Man of System
One sometimes hears arguments for busing or against private schools that say we need to prevent the best kids from leaving in order to benefit their less advantaged peers. I find such arguments distasteful. People should not be treated as means. I must confess, therefore, that I took some pleasure at the findings of a recent paper by Carrell, Sacerdote, and West:
We take cohorts of entering freshmen at the United States Air Force Academy and assign half
to peer groups designed to maximize the academic performance of the lowest ability students.
Our assignment algorithm uses nonlinear peer eff ects estimates from the historical pre-treatment
data, in which students were randomly assigned to peer groups. We find a negative and signi ficant treatment eff ect for the students we intended to help. We provide evidence that within our
“optimally” designed peer groups, students avoided the peers with whom we intended them to
interact and instead formed more homogeneous sub-groups. These results illustrate how policies
that manipulate peer groups for a desired social outcome can be confounded by changes in the
endogenous patterns of social interactions within the group.
I was reminded of Adam Smith’s discussion of exactly this issue in The Theory of Moral Sentiments:
The man of system, on the contrary, is apt to be very wise in his own conceit; and is often so enamoured with the supposed beauty of his own ideal plan of government, that he cannot suffer the smallest deviation from any part of it. He goes on to establish it completely and in all its parts, without any regard either to the great interests, or to the strong prejudices which may oppose it. He seems to imagine that he can arrange the different members of a great society with as much ease as the hand arranges the different pieces upon a chess-board. He does not consider that the pieces upon the chess-board have no other principle of motion besides that which the hand impresses upon them; but that, in the great chess-board of human society, every single piece has a principle of motion of its own, altogether different from that which the legislature might chuse to impress upon it. If those two principles coincide and act in the same direction, the game of human society will go on easily and harmoniously, and is very likely to be happy and successful. If they are opposite or different, the game will go on miserably, and the society must be at all times in the highest degree of disorder.
Do note that this discussion is not a critique of the paper which is very well done.