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Mailbag: Rebuttal to plastic bag ban study

February 19, 2013

This is a response to Jim Mouradick's letter connecting plastic bag bans increased death from food poisoning (see below). I was intrigued by the data to support this claim. I did a little research and was surprised when I saw a very similar letter on a blog written by a Steven Hayward.

As to the study, I found this rebuttal to the Klick and Wright study, from Dr. Tomas Aragon, San Francisco health officer. These are just three points from all they found. Pretty interesting food for thought from Aragon:

1. "The Klick and Wright study is classified as an ecological study; that is, if factor A (reusable bags) increased in a location, and then factor B (gastrointestinal bacterial infections) increase in the same location, therefore, factor A caused factor B. Drawing causal conclusions from this type of study is called an 'ecological fallacy.'"

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2. "In testing causal hypotheses, it is necessary to measure the outcome (gastrointestinal infections) and exposure to the putative cause (reusable bags) in the same persons. Because of their study design, this was not possible."

3. "In testing causal hypotheses, it is necessary to 'control for' alternative causal explanations (called 'confounders'). Because of their study design, this was not possible. For example, gastrointestinal bacterial infections are not only caused from contaminated food, but also from contaminated water, improper food-handling or -preparation, or from person-to-person spread (such as sexual activity, especially in men who have sex with men). In any causal study, investigators always adjust for the 'usual suspects.'"

The authors, Wright and Klick, also purportedly received funding from the American Chemistry Council — a trade group that represents plastic bag manufacturers.

It looks an awful lot like an industry-requested and -funded report that cherry-picked numbers for a specific headline outcome. Oh well, if it gets folks to air out and clean their disposable bags, I guess that's a good thing.

Editor's note: The Coastline Pilot learned after publication that portions of the letter in the Feb. 15 issue, "Trade-offs to environmentally friendly," previously appeared on a website, powerlineblog.com. The letter writer said he collaborated on the piece with another writer, who sent it to various blogs.

Chris Prelitz

Laguna Beach

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