Bettering that, Heiner Rindermann provides data aggregating results from multiple international student assessments given in various years to various students in several countries. This gets around potential isolated data errors and statistical anomalies. Jason Malloy pointed me to a site run by Volkmar Weiss presenting Rindermann's numbers, from which I sourced the nearly perfect correlation of .94 between the national IQ estimates of Rindermann and L&V.
But Weiss made some transcription errors. For Somalia, for example, Rindermann doesn't report any student assessment scores at all and assigns an adjusted IQ of 68 to the country. Weiss shows him reporting a 58 and V&H reporting an 84. But in IQ and Global Inequality, L&V give Somalia 68, the same score Rindermann assigns, as he has no assessment results for the country. I'm not sure what L&V estimated for Somalia in IQ and Wealth of Nations, which is where Weiss gets his V&H numbers, but such an enormous gap seems impossible, since in both cases Somalia is estimated from surrounding countries). There are other instances of similar errors on Weiss' site.
Knowing that Rindermann factored L&V's numbers into his own, it was clear the real relationship could not be that strong (the problem with Weiss' transcriptions aside). But how strong is it? I threw my hands up and said in lacking access to Rindermann's paper, I didn't know. Thankfully, my readers are more resourceful than I am. Bruce G. Charlton and Jason Malloy each sent me Rindermann's actual paper. The German professor explains how much weight L&V are given:
I calculated one total score for all cognitive ability studies (IQ, student assessment studies). Student assessment studies [PIRLS, PISA, and TIMSS in aggregate] were given a double weight in this total because they have newer and larger samples and they consist of more cross-national studies.The next step is to expand the 1-r gap by 50%, yielding a correlation of .91. It had initially struck me as curious (I don't quite miss everything) that Rindermann had estimates for as many countries as L&V did, since the assessments Rindermann used are administered in few third world countries and only a handful of middling countries.
As it turns out, for more than 100 countries (60% of the national total) Rindermann's only data source is L&V. There are no recorded results from any of the student assessments in these places. So most of Rindermann's figures are identical to the estimates L&V present in IQ and Global Inequality. Using only the student assessment converted aggregate scores for the countries where they are available and comparing them to L&V's estimates for the same countries (a total of 74) reveals a correlation of .85 (p=0).
This isn't surprising, as Lynn has shown that IQ results correlate with various international student assessments in the range of .81-.89. Well, Rindermann's aggregation of those assessments correlates with IQ scores at exactly the middle of that range.
Rindermann also presents his estimates with adjustments (five points subtracted from L&V estimates for countries without any actual data, age and participation rate adjustments for international student assessments). For the same 74 countries where assessment results are available, the correlation with L&V is a marginally stronger .86.
This increases my comfort in using L&V IQ scores. International student assessments, where available, are vigorously correlated with L&V. There is no apparent reason to presume L&V's IQ scores are less accurate than assessment results converted to IQ estimates are, and L&V provide numbers for more than twice as many countries as the international assessment scores do.
The data are here.