Comment on "Sexual maturation in relation to polychlorinated aromatic hydrocarbons: Sharpe and Skakkebaek's hypothesis revisited".

The description of the project suggests that the study was designed to investigate the effects of incinerator emissions on the local population in two suburbs of Antwerp, Belgium, Wilrijk and Hoboken. However, the study was part of a larger research project commissioned by the Flemish government to determine the feasibility and issues to be considered in developing environmental health monitoring. More particular, the study of Den Hond et al (2002) was designed to determine whether evaluation of biomarkers measured as part of the regular medical examination of adolescents at the end of their secondary education period would be feasible. We were asked by the Flemish government to review the results of this project (Cuijpers et al. 2000; Ghoetghebeur et al. 2000). We feel that the objectives and hypotheses underlying a feasibility study should not be convoluted with those relative to the hypotheses arising from specific concerns in certain a priori-defined regions. A major shortcoming of the design is the lack of randomness regarding both the study areas and the recruitment of the participants. The study areas were well-known polluted regions within the conurbation of Antwerp. This knowledge may have influenced the choice of tests to be performed. Researchers should be cautious regarding a priori choices of study areas, whether or not the sponsor influences the choice. The use of volunteers instead of randomly selected participants is another flaw, introducing an extra risk of confounding. As a consequence, for example, the proportion of boys to girls in the three study areas differed considerably: from 0.7 to 3.0. In this case there may have been a selection bias of adolescents in lesser physical condition who volunteered for examination. Reported results were the outcome of analyzing a multitude of associations among the empirical data; they did not emerge after a rigorous test of an a priori-formulated hypothesis, at least not to our knowledge. Such findings are valuable because they may generate hypotheses for further research. In this respect we agree with the authors’ closing sentence (Den Hond et al. 2002):