Economists devote strikingly little attention to immigration, so they tend to be suckers for the occasional study that comes along supporting their prejudices. For example, recent papers by Ottaviano and Peri claiming that lots of immigrants in California made the natives better off got lots of play.
George Borjas of Harvard couldn't replicate their findings, however, and now he's finally figured out why:
The Ottaviano and Peri data ... classify ... high school juniors and seniors as part of the "high school dropout" workforce. Their finding of immigrant-native complementarity disappears if the analysis excludes these high school juniors and seniors.
Things that seem too good to be true usually aren’t