To most general practitioners, the jewel in the cardiovascular prevention crown is secondary prevention. Patients are easily identified and of a limited number, their absolute risks are high, the interventions apparently straightforward and the impact significant. But how significant and for how long? The importance of determining long-term outcomes is highlighted by the 10-year follow-up study reported in this issue of the journal by Delaney et al (see page 1419).1 Their work is important: it is the first report of the longer-term value of a primary care based intervention in coronary heart disease (CHD).

EVALUATING THE EFFECTIVENESS OF INTERVENTIONS

Delaney et al remind us of evidence showing improved survival and fewer cardiac events among people with CHD 4 years after their enrolment in the intervention arm of a trial of nurse-led clinics in general practice.1 They now report outcomes after 10 years’ follow-up. Although more deaths had occurred in the control group after 10 years, differences between the intervention and control groups failed to reach statistical significance.1 The authors recognise that a possible dilution effect of the intervention might have arisen since, 1 year after the start of the original study, all patients had the opportunity of attending secondary prevention clinics.

Other studies have also encountered methodological difficulties when attempting to evaluate the effectiveness of prevention in CHD. These include the difficulties of maintaining uncontaminated control groups over time and the need to try to minimise contamination effects, particularly …