AMamum and F Willekens for their collaboration in the under- standing of the life table approach. Contributors: All authors participated actively in conception and design of the study or analysis and interpretation of data, in drafting

Objective To determine the effectiveness of commercially available magnetic bracelets for pain control in osteoarthritis of the hip and knee. Design Randomised, placebo controlled trial with three parallel groups. Setting Five rural general practices. Participants 194 men and women aged 45-80 years with osteoarthritis of the hip or knee. Intervention Wearing a standard strength static bipolar magnetic bracelet, a weak magnetic bracelet, or a non-magnetic (dummy) bracelet for 12 weeks. Main outcome measures Change in the Western Ontario and McMaster Universities osteoarthritis lower limb pain scale (WOMAC A) after 12 weeks, with the primary comparison between the standard and dummy groups. Secondary outcomes included changes in WOMAC B and C scales and a visual analogue scale for pain. Results Mean pain scores were reduced more in the standard magnet group than in the dummy group (mean difference 1.3 points, 95% confidence interval 0.05 to 2.55). Self reported blinding status did not affect the results. The scores for secondary outcome measures were consistent with the WOMAC A scores. Conclusion Pain from osteoarthritis of the hip and knee decreases when wearing magnetic bracelets. It is uncertain whether this response is due to specific or non-specific (placebo) effects. Manufacturers of permanent static magnet devices claim that they reduce pain in various conditions, including osteoarthritis. Worldwide sales were estimated at $5bn (£2.6bn, €3.8bn) in 1999. Osteoarthritis affects around 760 000 people in the United Kingdom, producing an estimated 3.02 million general practice consultations in 2000. If magnets were effective they would offer a cheap and probably safe treatment option. Some studies of permanent static magnets have found significant pain reduction 4–9 whereas others reported no effect. Major differences exist in the type and strength of magnets used, the conditions A chart showing flow of participants is on bmj.com The limits of medicine College Surgery, Cullompton, Devon EX15 1TG Tim Harlow general practitioner Peninsula Medical School (Primary Care), Exeter EX2 5DW Colin Greaves research fellow Peninsula Medical School, Tamar Science Park, Plymouth PL6 8BX Adrian White senior research fellow Peninsula Medical School (Complementary Medicine), Exeter EX2 4NT Liz Brown research assistant Edzard Ernst professor of complementary medicine