A little over a year ago, I published an op-ed in the New York Times titled “Farmers Markets and Food-Borne Illness.”
That op-ed was based on the findings of a similarly titled working paper of mine, which one of the New York Times editors had gotten wind of after I first discussed it on this blog during the summer of 2015.
In my op-ed, however, I mentioned that I would soon post an updated version of our paper. But things got busy, and though I worked quite a bit on it here and there, I did not get to finish it until a few weeks ago.
(And by “finish,” I mean “stop working on it until it is returned to us with reviewer comments about how to improve it before it can get published.”)
Here is the new version. The major innovation is that we now exploit both the longitudinal nature of the data as well as a source of plausibly exogenous variation for the number of farmers markets in a given state in a given year. This obviously makes for much stronger results than we used to have. Here is the abstract of this latest version:
Using administrative longitudinal data on all US states and the District of Columbia for the years 2004, 2006, and 2008-2013, we study the relationship between farmers markets and food-borne illness. We find a positive relationship between the number of farmers markets per million individuals and the number of reported (i) total outbreaks and cases of food-borne illness, (ii) outbreaks and cases of norovirus, and (iii) outbreaks of campylobacter per million in a given state-year. When we exploit weather shocks as a source of plausibly exogenous variation for the number of farmers markets per million, the majority of the aforementioned positive relationships persist. Allowing for small departures from the assumption of strict exogeneity of weather shocks, the relationship between farmers markets per million and the number of reported (i) total cases of food-borne illness as well as (ii) cases of norovirus per million turn out to be robust. Our estimates indicate that for every additional farmers market per million, there are six additional cases of food-borne illness per million, and that a doubling of the number of farmers markets in the average state-year would be associated with an economic cost of at least $220,000. Our core results are robust to different specifications and estimators as well as to deleting outliers and leverage points, and falsification and placebo tests indicate that they are unlikely to be spurious.