Yes, it was a Baysian not a mathematical argument.
That is a bit better, but even as a Bayesian argument it quietly rests on empirical priors which I find odd (as we’re about to see).
They are unless you have reason to believe the immigrants are above average.
In fact I do. gjm has listed a priori reasons to expect this. More empirically, I already know that epidemiologists talk about a “healthy immigrant effect”, which suggests that immigrants are selected (or indeed self-select) to be healthier & wealthier than the average for their home country. I’ve also seen people bringing up the selectedness of immigrants in arguments about race & IQ, to rebut observations that Third World immigrants tend to do better in their new homes than the estimated mean IQs of their home countries would suggest.
Comparing per-capita GDP with populations suggests we have decreasing returns to scale.
It does, but it is a very weak suggestion. The correlation is not that great to start with, and doesn’t account for other factors, like international differences in the working-age proportion of the population. Economists have tried to take a more systematic approach based on more involved regressions and/or fitting production functions, but the results here seem mixed, varying across industries and the level of aggregation.
(My own prior that increasing returns to scale occur in manufacturing — the class of industries, AFAIK, most important to a country’s development — seems broadly consistent with the available evidence. I may as well add that my point 3 invokes “increasing returns to scale & specialization” simply as an example, and the basic conclusion that there’s “[s]omething like a fallacy of composition” going on stands even if returns to scale are everywhere decreasing.)
One way to see the problem with Nancy’s argument is to consider the following question: If most people from country X want to move to country Y then wouldn’t it be easier for country Y to simply annex country X? You save on relocation costs and the people are now in country Y.
That is a bit better, but even as a Bayesian argument it quietly rests on empirical priors which I find odd (as we’re about to see).
In fact I do. gjm has listed a priori reasons to expect this. More empirically, I already know that epidemiologists talk about a “healthy immigrant effect”, which suggests that immigrants are selected (or indeed self-select) to be healthier & wealthier than the average for their home country. I’ve also seen people bringing up the selectedness of immigrants in arguments about race & IQ, to rebut observations that Third World immigrants tend to do better in their new homes than the estimated mean IQs of their home countries would suggest.
It does, but it is a very weak suggestion. The correlation is not that great to start with, and doesn’t account for other factors, like international differences in the working-age proportion of the population. Economists have tried to take a more systematic approach based on more involved regressions and/or fitting production functions, but the results here seem mixed, varying across industries and the level of aggregation.
(My own prior that increasing returns to scale occur in manufacturing — the class of industries, AFAIK, most important to a country’s development — seems broadly consistent with the available evidence. I may as well add that my point 3 invokes “increasing returns to scale & specialization” simply as an example, and the basic conclusion that there’s “[s]omething like a fallacy of composition” going on stands even if returns to scale are everywhere decreasing.)
I have little to add to what NancyLebovitz & skeptical_lurker have already said.