The YouNotSneaky blog does the math. From the lead-in:
Let's put on our annoying-economist hat and consider the question; if you consider a foreign national to be only 1/2 a human being (alright, alright, only 1/2 as "important") as a native citizen, are you justified in opposing immigration? After all, it takes a real jerk to argue that foreign people's welfare should not count at all. Suppose the foreigners are only 1/10th as important? Surely, if natives' welfare counts for ten times as much as that of foreigners, we would be justified in banning immigration since it may adversely affect the wages of the unskilled in US? Well, let's see…
It goes on from there, with some relatively heavy-lifting math for those of us out of academia for a while.
[Link via Marginal Revolution.]