Alex Tabarrok examines a Harvard Environmental Health paper linking Costco density to cancer rates—and why the correlation likely reflects confounding rather than warehouse clubs causing disease.
Does Costco Cause Cancer?
In December 2025, researchers led by Yazan Alwadi at Harvard’s T.H. Chan School of Public Health published a paper in Environmental Health that claimed to find that cancer incidence increased for people living closer to nuclear power plants in Massachusetts. In March, the same researchers published an expanded nationwide study claiming a similar result—this time looking at cancer mortality rates, rather than incidence—in Nature Communications. This was followed by a paper in the Journal of Exposure Science & Environmental Epidemiology that looked at associations of lung, breast, and colon cancers. Most recently, a study of total mortality, not just cancer, was published in the European journal Environmental Epidemiology.
The problem? Using the same methods pretty much everything causes cancer. An amazing takedown from Deric Tilson and Adam Stein:
For instance, living near a private four-year university is associated with a 15-fold increase in cancer mortality when compared to living near a nuclear power plant.
Costco has the largest effect of all the locations we have tested. Over 2.2 million cancer deaths can be attributed to Costco; that’s more than 20% of all cancer deaths between 2000 and 2018. Hot dogs, bulk spices, and reasonably priced clothes come with a cost.
What went wrong?
[The authors] chose nuclear power plants because a story could be built around that framework. When the researchers got positive results across our nation’s nuclear power plants, they didn’t check what their shiny new methodology would do using other landmarks. This is their pitfall: by taking the easy way out—getting results and making up a story around those results without double-checking their method—the authors could have no idea that what they were actually capturing was the methodology itself.
…The attributable number of deaths from this methodology is probably zero, but the attributable number of bad papers is at least four.