I think this is a bit of a roundabout argument. From the Philippines study:
We examine the effects of the policy changes on enrollment and graduation in other degree programs to determine whether increased migration prospects for nurses spurred new students to obtain postsecondary education or, instead, caused students to shift from other fields of study. While these results are relatively imprecise, they suggest that nursing enrollees primarily switched to nursing from other fields. This result helps to explain our large enrollment effects by clarifying that we are not estimating the elasticity of overall education to migration opportunities. Rather, the policy changes examined here were occupation specific, and individuals might be more elastic in switching between fields of study than making the extensive margin decision to enroll in higher education… While the enrollment effects were driven primarily by students switching from other degree types, students persisted to graduation at higher rates, leading to an overall increase in college graduates in the Philippines.
So they are finding exactly what you suggest, that people switch to the sector from other sectors, but they also find that if people hadn’t moved, they would have been less likely to graduate college, period. So if you see increases in the overall stock of college workers as an overall positive effect, the program did have an overall positive effect.
But in general, I don’t even think you need to appeal to that kind of reasoning, because brain drain is usually in jobs that are among the most valuable possible jobs for the country. (This is likely because those jobs are both the jobs that rich countries want to import, and also because they must be well-paid for the people to have the means to emigrate.) Medical workers are extremely valuable, so are engineers. It seems a little contrived to imagine that the sectors that lost out were comparably socially valuable.
I think this is a bit of a roundabout argument. From the Philippines study:
So they are finding exactly what you suggest, that people switch to the sector from other sectors, but they also find that if people hadn’t moved, they would have been less likely to graduate college, period. So if you see increases in the overall stock of college workers as an overall positive effect, the program did have an overall positive effect.
But in general, I don’t even think you need to appeal to that kind of reasoning, because brain drain is usually in jobs that are among the most valuable possible jobs for the country. (This is likely because those jobs are both the jobs that rich countries want to import, and also because they must be well-paid for the people to have the means to emigrate.) Medical workers are extremely valuable, so are engineers. It seems a little contrived to imagine that the sectors that lost out were comparably socially valuable.