When I arrived at the University of Minnesota in the fall of 2013, a few colleagues and I applied for a seed grant from the university’s Healthy Foods, Healthy Lives Institute by submitting a proposal to look at the impact of local and organic foods and food safety.
After working on it for almost two years, I am happy to finally be able to circulate my new paper titled “Farmers Markets and Food-Borne Illness,” coauthored with my colleague Rob King and my student Jenny Nguyen, in which we ask whether farmers markets are associated with food-borne illness in a systematic way. In order to answer that question, we use a US state-level panel data set for the years 2004, 2006, and 2008-2011 (i.e., the years for which we had a full data set).
Here is the abstract:
We study the relationship between farmers markets and food-borne illness in the United States. Using a state-level panel data set for the period 2004-2011, we find a positive relationship between the number of farmers markets per capita on the one hand and, on the other hand, the number of reported (i) outbreaks of food-borne illness, (ii) cases of food-borne illness, (iii) outbreaks of Campylobacter jejuni, and (iv) cases of Campylobacter jejuni. Our estimates indicate that a 1% increase in the number of farmers markets is associated with a 0.7% (3.9%) increase in the total number of reported outbreaks of food-borne illness (Campylobacter jejuni), and a 3.9% (2.1%) increase in the total number of reported cases of food-borne illness (Campylobacter jejuni) in the average state-year. Our estimates also suggest that a doubling of the number of farmers markets in the average state-year would be associated with an economic cost of over $900,000 in additional cases of food-borne illness. When controlling simultaneously for both the number of farmers markets and the number of farmers markets that accept SNAP benefits (i.e., food stamps), we find that they are respectively associated positively and negatively with reported food-borne illness outbreaks and cases. Our results are robust to different specifications and estimators, and falsification and placebo tests indicate that they are unlikely to be spurious.
This post is not about Gladwellian pabulum. Rather, it is about the econometric problem posed by outliers, whose presence of extreme-valued observations in a data set whose presence might cause problems of estimation and inference, and which a few colleagues have asked for a ‘Metrics Monday post on a few weeks ago.
Outliers cause estimation problems because they bias point estimates. They cause inference problems because they cause standard errors to be too large, thereby making it more likely that one will fail to reject a false null, i.e., a type II error. For example, if you collect data on a random sample of the population, the bulk of the people in your data might be between 18 and 80 years old, but you might also have someone in there who is 110 years old–that person is an outlier. Or the bulk of your sample might be making between $30,000 and $300,000 a year, but you might also have someone in there who makes $200,000,000 a year–that person is also an outlier. Continue reading →
This post is part of a continuing series on The Books that Have Shaped My Thinking.
It’s the summer, so I have time to read, both for work and for pleasure, and I have time to read books instead of just journal articles and blog posts. This made me realize that while a lot of my thinking has been shaped by things that I have read in journal articles (economics is an article-based field) and in blog posts (there is no better means of spreading important ideas quickly), a large part of my thinking has been shaped by books, which often contain more exciting ideas than journal articles–because they face less strict of a review process, books can be more daring in their claims, and thus have more chances of causing you to change how you view the world.
So I decided to write this series of posts on books that shaped my thinking. I talked about development books, about food and agriculture books, about economic theory books, and about econometrics books so far; this week I will talk about writing-related books. This will most likely be the last installment in this series–this blog is about the economics of agriculture, food, and development, I doubt anyone wants to know about the books that have shaped my thinking when it comes to fiction, or philosophy, or other things.
My view of writing advice has changed over the years. When I launched this blog almost five years ago, I loved to read and talk about writing. After a while, I realized that if most of the people who talk constantly about writing spent more time writing instead of talking about writing, they would be much more productive, and so I made the conscious choice to write instead of talk about writing. There are few exceptions to this rule, and here they are.
Some recommendations are very general; others are eminently personal. I just hope you can find one or two that will also shape your own thinking. I’m sure I am forgetting a lot of important books I have read and which have also shaped my thinking, but I made this list by taking a quick look at the bookshelves in my office.