Geographic variations in sperm counts: a potential cause of bias in studies of semen quality.
OBJECTIVE
To determine whether geographic variations in sperm counts might bias conclusions drawn from studies of semen quality.


METHODS
Reanalysis of published data from a meta-analysis of 61 studies from 1938 to 1990 that concluded a worldwide decline in semen quality over the last 50 years.


METHODS
Influence of geographic location on sperm counts.


RESULTS
Of 61 studies in the meta-analysis, only 20 included > or = 100 men. These 20 studies collectively comprised 91% of the total men studied. We focused our reanalysis on these 20 studies. Of the studies before 1970, all were from the United States and 80% were from New York. These studies represented locations with the highest sperm counts. In contrast, after 1970, 80% of the studies were from locations not represented earlier, including five studies from third world countries, where sperm counts were low.


CONCLUSIONS
Sperm counts vary dramatically among different geographic locations.
Fisch
H
H
Department of Urology, Squier Urologic Clinic, Columbia-Presbyterian Medical Center, New York, New York 10028, USA.
Goluboff
E T
ET
D015982:Bias; D006801:Humans; D007248:Infertility, Male / Q000453:epidemiology; D008297:Male; D012661:Semen / Q000502:physiology*; D013076:Sperm Count