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Friday, August 28, 2009

Installing an Extra Bathroom Won't Improve Your Child's SAT Scores

The New York Times uses this graph to show that kids from higher income families get higher average SAT scores:


Greg Mankiw (Harvard) responds in The Least Surprising Correlation of All Time:

Of course! But so what? This fact tells us nothing about the causal impact of income on test scores. ...  This graph is a good example of omitted variable bias. ...  The key omitted variable here is parents' IQ. Smart parents make more money and pass those good genes on to their offspring.

Suppose we were to graph average SAT scores by the number of bathrooms a student has in his or her family home. That curve would also likely slope upward. (After all, people with more money buy larger homes with more bathrooms.) But it would be a mistake to conclude that installing an extra toilet raises yours kids' SAT scores.

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Of course an elitist like Greg would ignore the impact of better schools, SAT prep courses,the impact of having a full stomach, teeth that don't hurt because the parents cant afford dental care, etc...

His promotion of a plutocracy and low taxes and higher barriers to keep this going will keep his ilk in power forever, and that is the way he likes it. Using silly arguements like bathrooms make me wonder what they are teaching at Harvard.

Posted by: California CPA | Aug 28, 2009 9:41:42 AM

Mankiw says that it's obvious that parents' IQ is correlated with their children's IQ, and that parents' IQ is correlated with parents' income. Therefore parents' income is correlated with their children's income via IQ. Advocates of social leveling studiously avoid this obvious fact because it invalidates their unstated assumption that outcomes of all sorts would be equal in the absence of discrimination.

Parents matter, both in nature and nurture. Parents want to give their children the best chance they can. Preserving that motivation is good for society. Destroying it through too many leveling policies will harm society.

Posted by: AMTbuff | Aug 28, 2009 10:50:11 AM

Anyone who thinks income is correlated with intelligence didn't grow up on Long Island.

Posted by: mike livingston | Aug 28, 2009 2:10:30 PM

A toilet of one's own promotes uninterrupted critical thinking.

Posted by: Jack Bogdanski | Aug 30, 2009 1:26:24 AM

ah-but IQ itself is probably related to wealth as well.

note that IQ is not all genes but also ahs a nuture element-one that the wealthy can provide better than the poor.

true that IQ will be static past age 16 or so..but that doesnt mean its genetic-it just means the nuture element happens before 16.

Posted by: george weiss | Aug 30, 2009 8:31:38 PM

These comments suggest to me that intellect is not positively correlated with posting comments on this blog.

Posted by: BigLaw Associate | Aug 31, 2009 10:11:50 AM