Infant mortality correlates more stongly with national average IQ as estimated in Lynn and Vanhanen's IQ and the Wealth of Nations than any other variable I'm aware of except for life expectancy (.84 and .85, respectively).
Does that relationship hold domestically? Unfortunately, the data on IQ by state are sparse. Tickle's results may approximate better than anything else out there--they correlate with GSP per capita at .53, white NAEP science scores at .63, Project Talent scores at .70, and my 'education index' (state's percentage of bachelor's degree and beyond minus state's percentage of less than high school diploma or equivalent) at a very high .86 (all statistically significant). They also correlate inversely with white infant mortality rates by state at .61 (unfortunately there are no recent data for white infant mortality in DC, the Tickle Test paragon).
The Tickle range for the fifty states plus DC is only five points, all presented as whole numbers. That the correlations remain so robust seems to evince the general accuracy of the results. I can only speculate on how they would be enhanced with numbers expanding out a couple of decimal places, but when I followed a friend's suggestion and contacted Tickle, a customer service rep told me it was proprietary information and then, sensing my frustration, advised me to see if I could find out more at Mensa. But he didn't expound and I found nothing there.