Table 3.

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

Events measured	Relative risk reduction (95% CI)*	No of eligible patients in a population of 100 000	No of patients needed to treat to prevent one event†	No of preventable events if all eligible patients receive intervention	Comments‡
Aspirin for patients at high risk of coronary or ischaemic cerebrovascular events
Total deaths over 1 year	17% (11% to 23%)21	3 00022	62	48	Trials 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 year	18% (12% to 24%)21		67	45 MI, stroke, or vascular deaths
Non-fatal MI over 1 year	35% (27% to 43%)21		68	44
Non-fatal stroke over 1 year	31% (21% to 41%)21		111	27
Control of hypertension
Total mortality over 4 years	16% (4% to 27%)23	17 88824	63	286	There is inconsistency in what constitutes controlled hypertension. Side effects can be a problem
CHD deaths over 4 years	25% (13% to 36%)23		100	179
Cerebrovascular deaths over 4 years	43% (21% to 58%)23		116	154
Advice on stopping smoking or nicotine replacement therapy
Total deaths over 1 year§	13%	30 00024	256	120	Relative 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%)25	1 50026	20	76	Patients 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 years	30% (15% to 42%)27	1 96828	29	69	Cholesterol 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 years	42% (17% to 54%)27		28	70
Major coronary events over 5 years	34% (25% to 41%)27		13	154
Statins for patients at low risk of coronary heart disease (primary prevention)
Total deaths over 5 years	22% (0 to 40%)29	1 39428	111	14	CHD 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 years	28% (−10% to 52%)29		155	9
CHD events over 5 years	31% (17% to 43%)29		41	34
Warfarin for stroke prophylaxis in non-valvular atrial fibrillation
Deaths over 1 year	33% (9% to 51%)30	1 90031	56	33	Side effects can be a problem and include intracerebral haemorrhage. Pooled data were from hospital based trials
Stroke events over 1 year	68% (50% to 79%)		33	58
Influenza vaccination for those aged >65
Deaths each year	68% (56% to 76%)32	15 70034	108	146	Effectiveness of vaccine depends on vaccine strain being sufficiently similar to epidemic strain
Influenza episodes each year	58% (26% to 77%)33		57	273

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.