The measured wage effect of the Mariel Boatlift flips with sample construction — no effect (Card) versus a 10–30% drop for dropouts (Borjas)

The 1980 Mariel Boatlift — roughly 125,000 Cuban refugees arriving in Miami over months — is the canonical natural experiment on how a sudden low-skill labor supply shock affects native wages. Serious economists working the same government data have reached flatly opposite headline conclusions, and the divergence tracks sample-construction choices rather than the event itself.

David Card's 1990 study found no measurable effect on less-skilled Miami wages. George Borjas (2015/2017) restricted the sample to high-school dropouts and reported a wage drop on the order of 10–30% for that subgroup. Giovanni Peri and Vasil Yasenov rebutted Borjas using the synthetic control method — built originally for Basque conflict economics — to construct a comparison "Miami," and argued that Borjas's result depended on "very drastic" sample restrictions, leaving only 15–20 Miami observations per year.

The structure recurs elsewhere in the vault: it is the same move as claim-soviet-emigre-career-premium-was-structural-not-ability, where holding ability constant and varying arrival year reverses a talent story into a market-structure story. Here one holds the event (the boatlift) constant and varies the comparison-group construction, and the sign of the conclusion flips. A separate line of attack argues the whole effect may be a measurement artifact rather than a real labor-market response — see claim-mariel-wage-effect-may-be-1980-census-methodology-artifact. Card's Mariel work later anchored his 2021 Nobel.