I thought it should maybe read "reduced infant mortality to numbers in cities/countries without toll booths" It wouldn't be a useful comparison beca

I thought it should maybe read "reduced infant mortality to numbers in cities/countries without toll booths" It wouldn't be a useful comparison because there are so many other variables at play in one country vs. another. Check the paper; it's very readable. Alternatively, know the following: The reason they chose their approach was because it gives them a "natural experiment" - by comparing the exact same area before and after EZPass, you get a fairly valid experiment with only a minimal number of variables to wrangle.