Correlation Does Not Imply Causation (Unless You Produce Energy)
August 3, 2015
By: M. Shane Harvey
A recent publication reported that researchers have found a “link” between hydraulic fracturing and increased hospitalization rates in the Marcellus shale drilling regions of Pennsylvania.
Cause for alarm? Not so fast.
Scientists and statisticians tell us that “correlation does not imply causation.” Two variables may be correlated (or “linked” as the media like to say) without one causing the other. One infamous example compares the correlation between global warming and the decrease in pirates:
As one can see from the graph, the correlation between global warming and piracy is a strong one. But, is the Earth warming because pirates are decreasing? Of course not. Unfortunately, though, many media sources and public interest groups often blur the line between correlation and causation when it comes to energy production.
Take, for example, the news story above regarding fracking and hospitalization rates in Pennsylvania (Link). If one were to read only the headline (“Fracking linked to Health Problems in Marcellus Shale Region, Study Finds”) one might conclude that fracking has been found to cause health problems. A closer read, however, tells a different story. According to the story, the authors of the study merely “suspect” that “many residents are exposed to many toxicants, noise, and social stressors due to hydraulic fracturing near their homes and this may add to the increased number of hospitalizations.” As the author (to his credit) goes on to point out:
Also, it’s worth noting that the study doesn’t actually prove hydraulic fracturing to be the cause of the aforementioned health problems, as the study’s author’s note that the increased hospitalized rates were observed over a relatively short period of time . . .
Sadly, this critical information on causation—buried in the final paragraph of the story as something “worth noting”—is completely absent from many similar news stories relating to health effects and energy production.
The coal industry has struggled with this problem for years. One particularly prolific researcher, Dr. Michael Hendryx, formerly with West Virginia University, has published over twenty papers claiming “links” between coal mining and various health problems, including cancer, heart disease, learning outcomes, birth defects and depression. However, Dr. Hendryx—who has avoided efforts to review his underlying data—has never explained the mechanism through which coal mining supposedly “causes” any of these problems.
Indeed, the “links” found by Dr. Hendryx often defy scientific explanation. One recent Hendryx paper suggested that dust generated by coal mining contained high levels (28%) of molybdenum that might be causing “tumor progression.” Geologists scoffed. Hendryx—a psychologist by training—was seemingly unaware that molybdenum is a very rare element, making up well below 1% of the composition of West Virginia’s soils. In other words, the notion that high levels of molybdenum were causing “tumor progression” in West Virginia’s coal fields was implausible.
Nevertheless, even though these and other concerns have been raised about the work of Dr. Hendryx (Link), media sources and anti-coal groups alike have cited his work for the proposition that coal mining is leading to health impacts in Appalachia.
Similar research is being aimed at the oil and gas industry. Recent studies have suggested “links” between fracking and various health issues. A June 2015 study, “Prenatal Outcomes and Unconventional Natural Gas Operations in Southwest Pennsylvania,” purported to find a correlation between fracking and “lower birth weights” for newborns. Notably, the researchers in the study clarified that the associations they found “do not imply causation and are hypothesis generating only.” Nevertheless, online publications like “EcoWatch” described the study as “alarming” and “disturbing.” See Link. Even the mainstream internet site “WebMD” covered the story, with little attention to the researcher’s disclaimers about causation. See Link.
We have been following the literature studying alleged health impacts from the coal and oil and gas industries. If you would like more information about these studies, please contact us.
This article was authored by M. Shane Harvey, Jackson Kelly PLLC.