My post below elicited a lot of response. One thing to point out though, which I want to emphasize: a higher proportion of smart people go to college now than in the past. How can this be? First, let's review the change in distributions of intelligence of those with college degrees (or higher) and those without. The first two charts show the proportions of WORDSUM scores for individuals with and without college degrees for two decades. I limited the sample to whites ages 30 and over. So for example in the period between 1974-1984, of those with college degrees and higher 26.8% scored 10 on WORDSUM. Among those without college degrees 21.8% scored 6. The error bars are 95% confidence intervals.
As you can see, the distribution of college graduates shifted. These results are in line with what I reported earlier; mean WORDSUM scores have dropped among college graduates. Now let's look at the proportion of those in each WORDSUM class who have college degrees. That is, what % of those who have a WORDSUM score of 10 have a college degree (or higher) in a given period. 1974-1984, 48.6% of those who scored a 10 or above on WORDSUM had college degrees of higher (whites, age 30 and up). 1998-2008 the corresponding value was 67.3%. Here's the chart:
As you can see, the whole curve simply shifts upward. Remember that a substantial proportion of college graduates are less intelligent than a substantial proportion of those without college degrees. While the proportion of the population with college degrees increased, and that increase was disproportionately from the higher end of the distribution, it was not such perfect sorting. The 30% who received college degrees were not the top 30% of the population. Consider these raw numbers from the GSS:
Only at the highest scores do college graduates outnumber those without college degrees in raw numbers. If fact, the top 20% of those without college degrees have higher WORDSUM scores than the bottom 50% of those with college degrees. And the ratio in raw numbers between these two in the GSS is almost even; that is, there are nearly as many people without college degrees who have WORDSUM scores above the 50th percentile of college graduates as those with college degrees. This is why WORDSUM scores have dropped among college graduates despite the fact that many more of the intelligent are now going to college and receiving bachelor's degrees. The modal WORDSUM score in the population is 6, and one must consider that the weight of each class matters a great deal in relation to the mean (lots of middle scores count more than a few high scores). Additionally the sorting is imperfect, and a substantial number of dumb are going to college and receiving degrees while a non-trivial number of intelligent are not receiving college degrees. Here is the distribution of WORDSUM scores for whites, of all ages, between 1974-2008:
Note: Those who do not have college degrees and have WORDSUM scores of 10 are disproportionately older. Among the age group 25-40 in 1998-2008 nearly 80% who score 10 have college degrees or higher.
