| NOTE: Research published 18 June 2003 reveals a dramatic link between sperm quality of men living in the US mid-west and exposure to three pesticides found commonly in water supplies. The review published in 1992 by Carlsen et al. (and described in OSF, Chapter 10) reported that human sperm count had fallen by approximately 50% over the past half-century. Their work was based on an analysis of 61 studies of sperm count patterns in individual places, most of them from Europe and North America with some from other regions, but mostly developed countries. This paper was followed by a series of critical reviews challenging the statistics and additional new reports of studies of sperm counts in specific places. According to these new studies, some places had experienced declines. Others had not. None reported increases of any significant magnitude. One of the striking patterns to emerge from these individual papers was how much geographic variation is evident today in sperm count in places from around the world. In the US, several studies indicated there had been no change in the recent past, and the US press then chose to take these studies as indications that there had been no change overall, ignoring methodologically superior studies from other places, particularly northern Europe (e.g., Parajinen et al., Irvine et al.). The US studies were from men who had volunteered for vasectomies, which introduces known biases into the sample. The willingness of the US press, especially Gina Kolata at the New York Times, to ignore scientific research conducted in other countries was breathtaking in its provincialism, especially given the industry ties of sources she cited and methodological weaknesses of the studies she gave weight. [Two investigative stories (article I, article II) subsequently criticized her reporting on this issue.] At the very least, the studies from other countries indicated that in those places changes had occurred. Because of their better methodologies, they raised questions about the significance and reliability of the US reports. There were also logical errors employed to refute Carlsen et al.'s analysis. Carlsen et al. had performed a statistical analysis and found an average decline, which they described in those terms. In the case of an average decline, not all places have to decline and indeed some can increase, yet still yield an average decline. That's the way of statistics. But industry spokespeople went farther. They took the individual studies showing no decline and used those cases to argue that Carlsen et al. were wrong. That is simply false logic. Carlsen et al.'s analysis allows for there to be variation among places. What is striking in this whole story, however, is that while many places show very large declines, and some places show no change, no places report large increases. Statistically, this implies there has been an average decline, precisely what Carlsen et al. found. The US studies finding no reports also raised some obvious questions which went unasked in media coverage of these issues. One of the studies found that there had been no change in New York or Los Angeles, even though there were dramatic differences between NY and Los Angeles, with NY average score being comparable to what had thought to be the historic range and LA being much lower. Given the historic mobility of the US population, it would be logical to assume at least some similarity in such a basic biological parameter. How had these differences arisen if there had been no change in either place? Additional analysis revealed that the statistical concerns raised in the initial criticisms would not have biased the work in a way that would have produced a "false positive." In other words, even if flawed, the original Carlsen et al. study was not flawed in a way that would suggest a positive result despite there being no underlying pattern. Using a more sophisticated statistical analysis, this new research strongly corroborated Carlsen et al. |
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