Response: Re: False-Positive Results in Cancer Epidemiology: A Plea for Epistemological Modesty

Extract

We are pleased to respond to the two letters to the Journal ( 1 , 2 ) concerning our commentary on false-positive findings in occupational and environmental cancer research. These letters only reinforce our call for scientific skepticism and epistemological modesty in the interpretation of epidemiological study results.

The commentary's first example of a likely false positive was the report of increased risk of breast cancer associated with high serum levels of the DDT [1,1,1,-trichloro-2,2-bis( p -chlorophenyl)ethane] metabolite DDE [1,1-dichloro-2,2-bis( p -chlorophenyl)ethylene]. Clapp and Kriebel ( 1 ) claim that lower blood levels of DDE over time account for the absence of increased risks of breast cancer associated with serum DDE levels in research studies subsequent to the initial publication of a positive effect, but this explanation is not supported by evidence. As shown in Table 1 of our commentary, virtually all of the blood samples used in the first four attempts to replicate ( 3–6 ) the initial positive study from New York ( 7 ) were collected before those used in the New York study, yet three of these studies showed a reduced risk of breast cancer among those with high DDE levels ( 4–6 ). Hence, although the conjecture proffered by Clapp and Kriebel ( 1 ) may be parsimonious, it is refuted by the epidemiological evidence.