Article Figures & Data
Tables
ACUTE SYMPTOMS LONG-TERM SYMPTOMATIC CONDITIONS CVD (PRIMARY PREVENTION) CANCER SCREENING (CANCER-SPECIFIC MORTALITY) SOCIAL SCREENING OR HEALTH PROMOTION Headache15: ASA or sumatriptan, NNT = 5 to 9 to be pain free at 2 hours Depression16: antidepressants, NNT = 7 to 9 for response in 6 weeks Statin17–20: NNT = 55 to 77 over 5 years (any CVD) Mammogram21,22: NNS = 377 to 2000 over 10 years Alcohol screening23: No evidence of benefit in heaviest drinkers Knee osteoarthritis24: intra-articular steroid, NNT = 3 to 5 for global improvement over 4 weeks Chronic neuropathic pain25,26: duloxetine or gabapentin, NNT = 6 to 8 at 3 months for reduction of ≥ 50% Metformin in diabetes27: NNT = 29 over 5 years (myocardial infarction) Fecal immunochemical testing28: NNS = 1200 over 10 years (assumed similar to fecal occult blood testing) Counseling on increased physical activity (single interventions)29–31: insufficient evidence of benefit Gout32: colchicine, NNT = 5 for ≥ 50% symptom free at 24 hours Headache33,34: tricyclic antidepressant or β-blocker, NNT = 4 to 8 over 6 months for reduction of 50% ASA35: NNT = 346 to 427 over 5 years (any CVD) Prostate-specific antigen36–38: NNS = 441 to 1410 over 10 years Family violence screening39: increased awareness but insufficient evidence for improved outcomes Benign positional vertigo40: Epley maneuver, NNT = 3 for symptom resolution Constipation (chronic)41: polyethylene glycol, NNT = 2 to 3 for resolution over 6 months Hypertension (≥ 160 mm Hg)42,43: treated, NNT = about 20 over 5 years (any CVD) Cervical cancer44,45: NNS unknown (but 1 in 500 women die of cervical cancer when screened every 3 years compared with 1 in 100*) Screening for obesity46,47: no evidence of improved outcomes (about 3 kg of weight loss with behavioural programs at 1 y; no evidence of improved patient outcomes) ASA—acetylsalicylic acid, CVD—cardiovascular disease, NNS—number needed to screen, NNT—number needed to treat.
↵* Data are based largely on national cohort and case-control studies that demonstrate a strong association between the introduction of screening and reduced incidence of cervical cancer. One cluster randomized controlled trial from rural India shows a 0.35 relative reduction in mortality with a 1-time screen.
CATEGORY ACUTE SYMPTOMS LONG-TERM SYMPTOMATIC CONDITIONS CVD (PRIMARY PREVENTION) CANCER SCREENING (CANCER-SPECIFIC MORTALITY) SOCIAL SCREENING OR HEALTH PROMOTION Estimated benefit NNT = about 5 NNT = about 7 NNT = about 40 over 5 years NNS = about 1000 over 10 years NNS = ∞ Encounters with benefit per year 176* to 720† 143‡ to 617§ 3.25‖ to 12¶ 0.13# to 0.36** 0 Encounters with benefit over 30 years 5280 to 21 600 4290 to 18 540 98 to 360 4 to 11 0 CVD—cardiovascular disease, NNS—number needed to screen, NNT—number needed to treat.
↵* Acute visits—conservative: Visits per year are based on 220 working days. Assuming 20 visits per day with 20% of visits having some acute symptom component, (220 × 20) × 0.2 = 880. Estimated NNT of 5 means 176 (880/5) encounters with benefit per year.
↵† Acute visits—better case: Visits per year are based on 240 working days. Assuming 30 visits per day with 50% of visits having some acute symptom component, (240 × 30) × 0.5 = 3600. Estimated NNT of 5 means 720 (3600/5) encounters with benefit per year. Assumptions minimizing benefit include no weekends, holidays, or evenings worked.
↵‡ Long-term symptomatic conditions—conservative: Based on a patient panel of 2000, assuming about 50% of patients have 1 continuing problem (note that some patients will have more and some will have none), then 2000 × 0.50 = 1000, with an NNT of 7 (1000/7 = about 143).
↵§ Long-term symptomatic conditions—better case: Visits per year are based on 240 working days. Assuming 30 visits per day with 60% of visits having some chronic symptom component, (240 × 30) × 0.6 = 4320. Estimated NNT of 7 means 617 (4320/7) encounters with benefit per year.
↵‖ Long-term CVD prevention—conservative: Using age 45 as the start of screening (knowing that is early) to age 75, that represents 32.5% of the population or 650 patients. Assuming all will be high enough risk to be offered at least 1 therapy, estimated NNT is 40 over 5 years (650/40 = 16.3 per 5 years, 16.3/5 = 3.25 per year).
↵¶ Long-term CVD prevention—better case: Using age 45 as the start of screening (knowing that is early) to age 75, assuming this demographic makes up 60% of the patient panel or 1200 patients, and assuming all patients will be high enough risk to be offered at least 1 therapy, with the most effective therapy (hypertension treatment), NNT is estimated to be 20 over 5 years (1200/20 = 60 per 5 years, 60/5 = 12 per year).
↵# Long-term cancer prevention—conservative: Assuming 650 eligible patients (as in CVD) and 2 maneuvers per patient, benefit would be 2 per 1000 over 10 years, or 1 in 500 over 10 years. So, we take 650/500 = 1.3 encounters with benefit over 10 years. That is 0.13 over 1 year or around 4 over 30 years.
↵** Long-term cancer prevention—better case: Using age 45 as the start of screening (knowing that is early) to age 75, assuming this demographic makes up 60% of the patient panel or 1200 patients, and assuming the best-case scenario (ie, mammography with NNS = 337 over 10 years), 1200/337 = 3.6 over 10 years. That is 0.36 over 1 year.
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