Epidemiologists should be able to tell us whether sperm quality has changed over time, or at least whether the quantity has changed. In 1992 Carlsen and colleagues concluded that sperm concentration per unit volume had fallen by 40% over the previous 50 years.1 This finding led to much speculation about the cause: oestrogens or pesticides in meat or water were the popular culprits (Horizon, “Assault on the Male: a Horizon Special,” BBC, 1993 Oct 31). In an article in this week's journal Bromwich and colleagues argue that Carlsen et al applied the wrong form of analysis and that an artefact explains nearly all of the putative “fall” (p 19).2

Before we enter the modern debate it is worth being reminded that the hypothesis of falling sperm quality attracted most attention in the 1970s, but it was debated in the peaceful obscurity of the specialist journals.3 Macleod and Wang temporarily silenced that debate; on the basis of a 10 year study of over 15000 men they concluded that there had been no decline.4 They considered all the large scale studies and compared them with their unique series from New York, where men had been analysed in the same laboratory for 30 years, with the same selection criteria and the same analytical methods being used.

This time around, …