在 Hacker News Daily 上看到的，原文標題比較漂亮：「Car Seats as Contraception」，在 Hacker News 上也有討論：「Car seats as contraception (ssrn.com)」，重點是作者之一 (David H. Solomon) 也有跑上去回應。
Abstract 的部份把重點都講出來了，1977 年美國通過汽車的兒童安全座椅法律，但大多數的汽車無法放下第三張座椅，這反而使得生第三胎的成本大幅提高 (需要買空間更大的車)，然後另外拉出資料分析因為法律而制止的車禍數量：
Since 1977, U.S. states have passed laws steadily raising the age for which a child must ride in a car safety seat. These laws significantly raise the cost of having a third child, as many regular-sized cars cannot fit three child seats in the back. Using census data and state-year variation in laws, we estimate that when women have two children of ages requiring mandated car seats, they have a lower annual probability of giving birth by 0.73 percentage points. Consistent with a causal channel, this effect is limited to third child births, is concentrated in households with access to a car, and is larger when a male is present (when both front seats are likely to be occupied). We estimate that these laws prevented only 57 car crash fatalities of children nationwide in 2017. Simultaneously, they led to a permanent reduction of approximately 8,000 births in the same year, and 145,000 fewer births since 1980, with 90% of this decline being since 2000.
濃濃的政治不正確感 XD