Table 3

Primary care interventions: relative risk reductions, eligible patients, numbers needed to treat, and total number of preventable deaths or events

Events measuredRelative risk reduction (95% CI)*No of eligible patients in a population of 100 000No of patients needed to treat to prevent one eventNo of preventable events if all eligible patients receive interventionComments
Aspirin for patients at high risk of coronary or ischaemic cerebrovascular events
Total deaths over 1 year17% (11% to 23%)213 000226248Trials reviewed varied in length of follow up. Largest benefits were seen in first year of follow up. Side effects can be a problem and include intracerebral and gastrointestinal haemorrhage
Vascular deaths over 1 year18% (12% to 24%)216745 MI, stroke, or vascular deaths
Non-fatal MI over 1 year35% (27% to 43%)216844
Non-fatal stroke over 1 year31% (21% to 41%)2111127
Control of hypertension
Total mortality over 4 years16% (4% to 27%)2317 8882463286There is inconsistency in what constitutes controlled hypertension. Side effects can be a problem
CHD deaths over 4 years25% (13% to 36%)23100179
Cerebrovascular deaths over 4 years43% (21% to 58%)23116154
Advice on stopping smoking or nicotine replacement therapy
Total deaths over 1 year§13% 30 00024256120Relative risk reduction extrapolated from a UK cohort and may be an overestimate because of confounding
Angiotensin converting enzyme inhibitors for patients with heart failure
Total deaths over 90 days§23% (12% to 33%)251 500262076Patients in many of the trials were younger than those in the general population
Statins for patients at high risk of coronary heart disease (secondary prevention)
Total deaths over 5 years30% (15% to 42%)271 968282969Cholesterol lowering is only one of many possibilities to reduce CHD risk. Stroke risk may also be reduced. Essentially, all the deaths prevented were coronary deaths
All coronary deaths over 5 years42% (17% to 54%)272870
Major coronary events over 5 years34% (25% to 41%)2713154
Statins for patients at low risk of coronary heart disease (primary prevention)
Total deaths over 5 years22% (0 to 40%)291 3942811114CHD rates have been falling in UK for two decades. This must be taken into account when making projections of population benefits from interventions such as lipid lowering drugs
CHD deaths over 5 years28% (10% to 52%)291559
CHD events over 5 years31% (17% to 43%)294134
Warfarin for stroke prophylaxis in non-valvular atrial fibrillation
Deaths over 1 year33% (9% to 51%)301 900315633Side effects can be a problem and include intracerebral haemorrhage. Pooled data were from hospital based trials
Stroke events over 1 year68% (50% to 79%)3358
Influenza vaccination for those aged >65
Deaths each year68% (56% to 76%)3215 70034108146Effectiveness of vaccine depends on vaccine strain being sufficiently similar to epidemic strain
Influenza episodes each year58% (26% to 77%)3357273
  • MI=myocardial infarction; CHD=coronary heart disease.

  • *Reduced risk of death or events for those receiving the intervention compared with those not receiving it

  • †Calculated from the attributable risk reduction presented in the appendices available on the BMJ website.

  • ‡References for these statements appear in the appendices available on the BMJ website.

  • §We were unable to calculate other events from the studies that we used.