In my role as Health Officer of San Francisco I received a flurry of concerned calls about a research study that claimed that the 2007 San Francisco ban on plastic bag resulted in an immediate, very large increase in foodborne illnesses and deaths. From their conclusions:
“We examine deaths and emergency room admissions related to these bacteria in the wake of the San Francisco ban. We find that both deaths and ER visits spiked as soon as the ban went into effect. Relative to other counties, deaths in San Francisco increase by almost 50 percent, and ER visits increase by a comparable amount.”
Here is the introduction to a memo I composed in response to this study:
“This memo is to respond to a recent unpublished research paper concluding that the San Francisco ban on plastic bags has led to an increase in bacterial foodborne illnesses and deaths. This paper is from Jonathan Klick and Joshua D. Wright from the University of Pennsylvania Institute for Law & Economics. Based on our review of this paper, and our disease surveillance and death registry data, the Klick & Wright’s conclusion that San Francisco’s policy of banning of plastic bags has caused a significant increase in gastrointestinal bacterial infections and a “46 percent increase in the deaths from foodborne illnesses” is not warranted.”
My full memo is here:
The Klick study I read is here:
Reading their article and responding to public concerns reminded me of several things:
- Law professors and epidemiologists use difference study designs to infer causality.
- Research studies with alarming conclusions can alarm the public – so be cautious.
- Reach out and collaborate with experts in other disciplines — the science is better.
- Ecological study designs should not be the basis of exposure-disease causal inference when better methods are available. If used, stress the limitations and assumptions.
- Assessing the health impacts of policies is called Health Impact Assessments (HIAs). Consider using the Institute of Medicine HIA Framework.