title: Geographic variations in sperm counts: a potential cause of bias in studies of semen quality.
abstract: 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.
authors.affiliation: Department of Urology, Squier Urologic Clinic, Columbia-Presbyterian Medical Center, New York, New York 10028, USA.
authors.forename: H
authors.initials: H
authors.lastname: Fisch
authors.forename: E T
authors.initials: ET
authors.lastname: Goluboff
mesh_terms: D015982:Bias; D006801:Humans; D007248:Infertility, Male / Q000453:epidemiology; D008297:Male; D012661:Semen / Q000502:physiology*; D013076:Sperm Count