Medical journals are often accused of being remote from the real world. They present the results of trials conducted on highly selected patients in ideal circumstances. They view the world from London, Boston, or Chicago unaware that in Peioria or Harrogate patients don't turn up, won't comply with treatments, and scoff at “patient centredness” and that the local hospitals are falling down and run by people who until yesterday were running sewage plants. Well, this issue has a whiff—even a stink—from the real world.

The BMJ has published many studies suggesting that serum screening for Down's syndrome in pregnant women is …