I have come to notice that the Black-White gap is in a state of perpetual decline. Every couple of years a report comes out showing that the mean score difference has narrowed and, yet, every time I compute the standardized difference, the difference comes out to about 1 +/- 0.2 SD. As example of this score narrowing, Steve Sailer recently pointed to the newly released 2011 PIRLS reading results. The 2011 PIRLS reading gap is only 53 points — on a metric that has international standard deviations of 100. This is down from 57 points in 2006 and 63 in 2001!
Yet when I compare the standardized gap between 2001 and 2006 I find exactly no decline, because while the gaps declined from 63 points to 57 points, the pooled standard deviations also declined from 74 to 68 (i.e., the variance was decreased). Unfortunately, I have been unable to find standard deviations for 2011 — so I can’t determine if there was a narrowing in the standardized difference or a narrowing in variance. The pooled SD would have had to decline to 63 in 2011 from 68 in 2006 for the standardized difference to remain 0.84 given the score difference (of 53 points). A safe bet would be the the 2011 pooled B/W standard deviations were similar to those in 2001 and 2006 (mean 71) and so that the standardized difference was 0.74 SD; if so, the gap would have declined 12% in the last 10 years.