Papers
Commentary: Importance of empirical evidence
BMJ 1994; 309 doi: https://doi.org/10.1136/bmj.309.6946.22 (Published 02 July 1994) Cite this as: BMJ 1994;309:22
- N Keiding,
- A Giwercman,
- E Carlsen,
- N E Skakkebaek
- Statistical Research Unit, University of Copenhagen, Panum Institute, DK- 2200 Copenhagen, Denmark University Department of Growth and Reproduction, Rigshospitalet 5064, DK-2100 Copenhagen.
Bromwich et al point out that the distribution of sperm count is skewed to the right and that if a differential selection of skewed distributions is applied over the years this will bias the observed time trends. Both of these assertions are correct; indeed, in all 16 of the 61 publications cited in our original overview for which both median and mean were given the median was smaller than the mean, confirming the skewness.1
Bromwich et …