If the Holocaust is what we are told, this is a pretty unlikely finding. We should expect higher average IQ from survivors (compared to other Jews) because all these activities exhibit or are correlated with intellectual ability:
- Avoiding capture.
- Escaping prison camp.
- Surviving disease.
- Surviving execution.
- Convincing non-Jews to protect or spare you.
- Being selected for work instead of execution.
That last one is literally selection. That is, the Germans are said to have selected the Jews who were the most physically and mentally fit people to live, and all the rest had to go to gas chambers or some other death. A strictly eugenic process!
These are all good reasons to expect higher average IQ among survivors. On the flip side, there
could be some contrary factors:
- The category of Holocaust survivors sometimes includes many Jews who were never in any danger. This could lessen the IQ selective effect.
- Many survivors claim to have survived gassings and executions by some miracle or accident. This could lessen or even reverse the IQ selective effect, but it's too unserious to consider.
- The Holocaust overwhelmingly concerned Ashkenazi Jews, whereas the comparison set could include many Sephardic or Mizrahi Jews. This meta-analysis appears to have used "European-born Jews" for comparison, plus some studies were done in the U.S. and some in Israel, which should eliminate that issue.
- The children of survivors would inherit their parents' intelligence without being considered survivors themselves. However, this meta-analysis used studies where Jews were compared within their own age group, not across generations.
Therefore Holocaust survivors have substantial reason to be of higher average IQ and there is little reason for the effect not to appear. Here are the findings from the paper:
In the set of five nonselect samples, containing 769 participants, the difference in cognitive functioning between Holocaust survivors and comparisons was not significant. The size of the combined effect was a Cohen’s d of 0.10, p = .21, 95% CI [0.06, 0.26] (see Table 8). In the set of four select samples, containing 250 participants, the difference in cognitive functioning between Holocaust survivors and comparisons was significant. The size of the combined effect was a Cohen’s d of 0.43, p < .01, 95% CI [0.17, 0.69]. The fail-safe number for the combined effect size was 6. The funnel plot showed that there was some publication bias. One study had to be trimmed and replaced, resulting in an adjusted, significant effect size of d = 0.39, 95% CI [0.15, 0.62]. In select samples, in contrast to nonselect samples, Holocaust survivors functioned more poorly than did comparisons on cognitive tasks.
If I'm interpreting this correctly, the first group of studies found no difference in IQ, the second group of studies found survivors had -5.9 IQ points, and the combined effect was -1.5 IQ points but within the margin of error. These findings are the reverse of what we should expect.
However, does revisionism better predict this result? Not necessarily. If revisionists say that millions of Jews did die, most of the above factors still apply. So other selective factors need to be considered.