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.
review published in 1992 by Carlsen
(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.
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.
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
et al., Irvine
et al.). The US studies were from men who had volunteered for
vasectomies, which introduces known biases into the sample.
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.]
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.
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.
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.
US studies finding no reports also raised some obvious questions
which went unasked in media coverage of these issues. One of the
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?
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.