numbers needed to treat

Here are some examples of Numbers Needed to Treat, found at the Bandolier web site (http://www.jr2.ox.ac.uk/bandolier/index.html).

Prevention of post-operative vomiting using Droperidol, NNT=4.4. For every four or five surgery patients treated with Droperidol, you will see one less vomiting incident on average.

Prevention of infection from dog bites using antibiotics, NNT=16. For every 16 dog bites treated with antibiotics, you would see one fewer infection on average.

Primary prevention of stroke using a daily low dose of aspirin for one year, NNT=102. For every hundred patient years of treatment with aspirin, you will see one fewer stroke on average.

Here's another example from the British Medical Journal (Freemantle 1999: 318(7200); 1730-1737). Prevention of cardiac death using beta blockers among patients with previous myocardial infarction, NNT=42. For every 42 patients treated for two years with beta blockers, you would see one fewer death. This is superior to treatment with antiplatelet agents (NNT=153), Statins (NNT=94), or Warfarin (NNT=63), but not as effective as thrombolysis and aspirin for 4 weeks (NNT=24).