  We collected marathon performance data from a systematic sample of elite and
sub-elite athletes over the period 2015 to 2019, then searched the internet for
publicly-available photographs of these performances, identifying whether the
Nike Vaporfly shoes were worn or not in each performance. Controlling for
athlete ability and race difficulty, we estimated the effect on marathon times
of wearing the Vaporfly shoes. Assuming that the effect of Vaporfly shoes is
additive, we estimate that the Vaporfly shoes improve men's times between 2.0
and 3.9 minutes, while they improve women's times between 0.8 and 3.5 minutes.
Assuming that the effect of Vaporfly shoes is multiplicative, we estimate that
they improve men's times between 1.4 and 2.8 percent and women's performances
between 0.6 and 2.2 percent. The improvements are in comparison to the shoe the
athlete was wearing before switching to Vaporfly shoes, and represents an
expected improvement rather than a guaranteed improvement.
