## Wednesday, December 29, 2010

### Teacher Value

Last week Kevin Drum posted about a paper (pdf file, may be behind a paywall) by Eric Hanushek which estimates that a teacher one standard deviation above mean will improve the present value of a typical student's lifetime earnings by a substantial amount (\$20000 with one set of assumptions). If correct these estimates would justify considerable effort and expense improving the average quality of teachers. However as readers of this blog know I doubt teachers make much difference. This paper has not convinced me otherwise.

The paper's estimates depend on a number of extremely debatable assumptions. Even worse it appears to contain a blatant error. One reason teachers don't matter much in the long run is the measured effects they do have tend to be temporary, fading away with time. Hanushek recognizes this and defines (p 14-15) a depreciation variable theta. But he does not appear to realize the effects are cumulative. After n years the effects of a particular teacher (as measured by achievement tests) are reduced by a factor of (1-theta)**n. But Hanushek assumes (1-theta) of the effect is permanent. Since theta is estimated as .3-.6 this makes a huge difference in his calculations. So, even granting the assumptions in his model, correctly computed the effect of an above (or below) average teacher will be much less than claimed.

The cumulative nature of this effect is clearly stated in one of the papers Hanushek cites Estimating Teacher Impacts on Student Achievement: An Experimental Evaluation ((c) 2008 Kane and Staiger, p.4):

Finally, in the experimental data we found that the impact of the randomly assigned teacher on math and reading achievement faded out at a rate of roughly 50 percent per year in future academic years. In other words, only 50 percent of the teacher effect from year t was discernible in year t+1 and 25 percent was discernible in year t+2. ...

## Friday, December 24, 2010

### Highland Diner RIP

In the 90s I used to eat dinner regularly in the Highland Diner on Highland Avenue (Route 9) in Ossining. I have fond memories of the place. It appeared to be a venerable Ossining institution. The author John Cheever who lived in Ossining in the later part of his life used to hang out there. Cheever died in 1982 before I moved here but the restaurant still had pictures of him.

The restaurant changed hands about 10 (?) years ago. I continued to eat there sometimes but it was never quite the same. It has since operated under several names and owners but apparently (despite what appeared to be considerable expenditure on renovations) has struggled financially. Perhaps because one of the things I liked about the place, that it was rarely crowded, didn't change. Its latest incarnation was as the Olympic Diner but when I went to eat there last Saturday I found it closed. As with Charlie Brown's I had not noticed signs of distress (unlike an earlier incarnation which was open for a couple of weeks in the summer without AC before finally giving up the ghost). There were signs saying it would reopen with new management. Perhaps things will work out better this time. However I suspect the traditional diner business model is not as viable as it used to be and some changes may be needed. Which is always tricky as you may lose the old customers without getting enough new ones.

## Saturday, December 18, 2010

### Millennium Trilogy

I just read the Millennium Trilogy a series of three thrillers by the Swedish journalist Stieg Larsson. Obviously the books have been around for a while but only recently became available (without reserving them) at local libraries.

In my view the books aren't all that good. They are quite long (the first is 644 pages in paperback, the second and third 503 and 563 pages in hardcover) and seemed uneven to me dragging in places. The second book contained a number of implausible coincidences and a preposterous (even by the standards of the genre) escape from peril. The Lisbeth Salander character is quite unrealistic. Annoyingly she is portrayed (briefly, again in the second book) as a brilliant chess player by an author who clearly knows nothing about chess. The books are set in Sweden and contain a number of obscure local references. This is partly the fault of the translation, for example it would have been simple to give the approximate value of the Swedish kronor in dollars when it was first mentioned.

I wouldn't say the books are terrible. I did find them interesting in parts and I have certainly read worse. However I have also read many thrillers as good or better that have not achieved the same popularity. The ingredients of popular success are a bit mysterious. In this case I suspect Larsson's untimely death contributed as did the somewhat exotic setting (Sweden). Perhaps in some way the books resonate with a portion of the reading public. And of course once a certain level of success is achieved a snowball effect can take over.

In summary these are the sorts of books you might read on say an airplane flight if nothing better was available but not really anything I would recommend making a special effort to read.