Once Again–Correlation Does Not Equal Causality

Much press has been generated by a University of West Virgina Medical School press release about research on PROA and PFOS and cholesterol among children in the Mid-Ohio Valley.

The press announcement concerns a study previously done and reviewed by the C8 Science panel in 2009.  It is just now being published in a Pediatric journal.  Basically the study measured cholesterol levels and levels of PFOA and PFOS.  The Scientific Panel report had this to say:

“Interpretation of these results is made difficult by the cross-sectional design of our study, which prohibits knowing whether an increase in cholesterol (or LDL cholesterol) may have followed or preceded an increase in PFOA or PFOS.  The mechanism by which these chemicals might be related to cholesterol in humans is not known. These data alone cannot prove whether the PFOA and PFOS differences in these children caused the observed shift in cholesterol, or whether there is another explanation.”

Note the statement, “These data cannot prove…the observed shift in cholesterol.”  However, many headlines trumpeted  lines like:  “Cholesterol linked to Teflon”, leading consumers to believe that cooking in nonstick cookware will cause their kids cholesterol to increase.  This is what is known as causality and not correlation.  Correlation does mean something causes it.  It may be that high cholesterol levels cause children to accumulate PFOA.  Or it could be that these kids diet is high in fats.

An economics professor presented two graphs to her class–one with the increase in salaries for Presbyterian ministers from 1930-1980; the second with the price of Scotch whiskey over the same time period. The lines on the two graphs aligned perfectly.  “Which caused which?” she asked.  “Did the minister’s pay cause the whiskey to increase, or the price of whiskey caused the salary increases.”

Of course there was no causality. Both salary and hooch prices were affected by inflation.

Also the study linked PFOS, a chemical which is not used in any nonstick coating manufacturing at all.   It is also interesting to note that PFOA levels are found through nature, including polar bear populations.  We are fairly sure the bears aren’t using nonstick cookware.  The PFOA may be there in the bears, but it’s not from cookware.

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