Thursday, August 30, 2007

Grading for Class Participation: A Moral Issue

It is common for professors to base a student's grade in part on the degree to which he participates in class discussion. This policy seems to me to raise serious moral issues. The grades I give my students purport to measure how much of what is taught in the class they know. By giving a higher grade to those who participate more I am bribing them to help me to teach the class. To put the point more strongly, I am getting them to help me by offering to lie to their future employers about them, to overstate how much they learned as a reward for their assistance.

This objection would not apply if I were using their classroom participation merely as evidence of how much they had learned, grading them up for participation that provided positive evidence, down for participation that provided negative evidence. But that is not what professors who give credit for class participation do, or say they do.

Wednesday, August 29, 2007

Climate Complications

Freeman Dyson has an interesting essay on heresy, global warming and much else. He argues that we don't know nearly enough to predict what will happen to climate, what the human contribution to climate change is, or whether likely changes are on net good or bad. In particular, we do not understand the biological part of the equation very well--the effect of increases in CO2 or changes in human land use on the amount of carbon tied up in topsoil.

When I point out how small the predicted effects are of global warming--a few degrees increase in temperature and a foot or so in sea level over the next century--a common response is that the average effects understate the costs. Dyson implies the opposite conclusion:

In humid air, the effect of carbon dioxide on radiation transport is unimportant because the transport of thermal radiation is already blocked by the much larger greenhouse effect of water vapor. The effect of carbon dioxide is important where the air is dry, and air is usually dry only where it is cold. Hot desert air may feel dry but often contains a lot of water vapor. The warming effect of carbon dioxide is strongest where air is cold and dry, mainly in the arctic rather than in the tropics, mainly in mountainous regions rather than in lowlands, mainly in winter rather than in summer, and mainly at night rather than in daytime. The warming is real, but it is mostly making cold places warmer rather than making hot places hotter. To represent this local warming by a global average is misleading.

One of the best bits of the essay deals not with global warming but with the tension between "naturalist" and "humanist" views of the world:

Here I must confess my own bias. Since I was born and brought up in England, I spent my formative years in a land with great beauty and a rich ecology which is almost entirely man-made. The natural ecology of England was uninterrupted and rather boring forest. Humans replaced the forest with an artificial landscape of grassland and moorland, fields and farms, with a much richer variety of plant and animal species. Quite recently, only about a thousand years ago, we introduced rabbits, a non-native species which had a profound effect on the ecology. Rabbits opened glades in the forest where flowering plants now flourish. There is no wilderness in England, and yet there is plenty of room for wild-flowers and birds and butterflies as well as a high density of humans. Perhaps that is why I am a humanist.

Tuesday, August 28, 2007

Affirmative Action, Richard Sanders and Thomas Sowell

A recent op-ed in the Wall Street Journal discusses research by Richard Sanders suggesting that affirmative action by law schools actually reduces the number of black lawyers. The argument, and the evidence, is elegant and persuasive. If you classify law students by academic credentials and what tier law school they go to, black students and white students have about the same bar passage rate--a black who goes to (say) a second tier law school is about as likely to pass the bar as a white at a similar law school with similar academic credentials. But if you classify students only by academic credentials, blacks have a much lower bar passage rate than whites.

Sanders' explanation is a mismatch between students and schools. Black students do not, on average, end up in the same law schools as white students with the same credentials. Law schools compete to get black students, there aren't enough well qualified ones, so elite schools accept black students with qualifications well below those they require for white students. The result is that many black students end up in schools and classes they are not qualified for, learn little, and fail to pass the bar--students who would have done better in a less elite school designed for students more like them. He estimates that a race blind admission policy would result in fewer black students going to law school but more passing the bar.

After reading the op-ed, I told my wife about it. She pointed out that the argument was not original with Sanders. Almost twenty years ago, in his very interesting Choosing a College: A Guide for Parents and Students, Thomas Sowell made precisely the same point in the context of colleges rather than law schools. Black students at MIT had math scores well above the national average but far below the average for white students at MIT; they would have gotten a better education at a less elite engineering school.


Saturday, August 25, 2007

Do Barack Obama and Hilary Clinton Read This Blog?

Back in December of 2005, I suggested that, in order to win over libertarian voters, “At the very least, prominent Democrats should come out in favor of the federal government respecting state medical marijuana laws, as it has so far refused to do.”

According to Reason’s Hit and Run Blog, “Barack Obama has joined the seven other Democratic presidential candidates in promising to call off the DEA's medical marijuana raids if he's elected.”

Nice to know someone was listening.


Tuesday, August 21, 2007

Internet in Hotels—a Puzzle

In my experience, low and medium priced hotels/motels usually provide a free internet connection, high priced ones usually charge for it. This seems to be true not only in the U.S. but in Europe as well, although that conclusion is based on less data—one fancy hotel in Helsinki, one each less fancy in London and Paris.

Does the pattern hold in general? If so, why? The obvious guess is that it has something to do with price discrimination, but I'm not sure just why it makes more sense to price discriminate against internet users in expensive hotels than in inexpensive ones.

Low Cost Cooling

A common hot weather strategy, especially for people living in big old houses without air conditioning, is to open windows at night when it is cool out, close them in the morning.

It should be straightforward to automate the procedure, using windows or vents that can be set to open when the temperature outside is cooler than the temperature inside, close when it is warmer, with fans to increase the airflow when desired. I would expect both the capital cost and the operating cost of such a system, used to replace or supplement air conditioning, to be trivial relative to the cost of air conditioning itself.

Yet I do not think I have ever seen such a system. Have I missed it? Or is there some non-obvious problem with the idea?

[The reason I have not been posting is that I've been travelling].