Mr. Dalliard writes:
You could make an immigrant selection argument about Italy. It’s not only that in the period of high European immigration to America immigrants were probably IQ-selected. You should also consider the fact that lots of immigrants returned to Europe. 55 percent of Italian immigrants went back in 1908-1924, compared to 10-20 percent of North-Western Europeans.
Emigration from America was probably correlated negatively with IQ. Moreover, northern Italians were somewhat less likely to return than southern Italians, but they were of course only 15 percent of all Italian immigrants (the difference in repatriations between Northern and Southern Italy was about 7 percentage points in 1908-1924). Italian immigration was also highly male-biased compared to NW European immigration, which may also have had a selective effect.
Irish immigrants rarely returned to Europe in 1908-1924, so a selection argument is less persuasive with respect to them, at least for that period.
The correlation between ethno-national rates in staying in America and Lynn’s national IQs is 0.34. Italy (IQ 102) and Ireland (IQ 92) are the biggest outliers — if you exclude them, the correlation is 0.56. (I put Jewish IQ at 110, and used the closest equivalents for groups with no reported IQs.)
Maybe. I noted, a while ago, one way to test Lynn’s natioracial hereditarian hypothesis, a hypothesis which predicts inter-generational transference of traits across time and space: look at the association between immigrant performance, across generations, across nations, on international tests and the national IQs of the countries from which the immigrants hail. “Error”, due to idiosyncratic factors, such as immigrant selectivity, should somewhat cancel out when looking across scores of nations. I began doing this in my post: Do National IQs predict immigrant performance across Europe?. Oddly, no one cared to follow up on this — despite this, migrant performance, being at the very heart of the issue.
Doing this does not require restricted access data. And the analyses involved are not technically difficult. All of the international surveys can be downloaded online. And there is a now free IEA International Database (IDB) Analyzer which simplifies cross national analyses. Such an analysis would only be time/energy consuming.