Table 1 Characteristics of the included studies and of the number needed to treat (NNT)
From: Number needed to treat (NNT) in clinical literature: an appraisal
Characteristics | Meta-analysis (n = 23) | RCT (n = 17) | Cohort (n = 9) | Nested case–control (n = 2) | Overall (n = 51) | |||||
|---|---|---|---|---|---|---|---|---|---|---|
Journal | ||||||||||
JAMA | 9 | (39.1%) | 4 | (23.5%) | 2 | (22.2%) | 2 | (100.0%) | 17 | (33.3%) |
Lancet | 6 | (26.1%) | 7 | (41.2%) | 1 | (11.1%) | 0 | (0.0%) | 14 | (27.5%) |
Am J Med | 2 | (8.7%) | 0 | (0.0%) | 2 | (22.2%) | 0 | (0.0%) | 4 | (7.8%) |
Other | 6 | (26.1%) | 6 | (35.3%) | 4 | (44.4%) | 0 | (0.0%) | 16 | (31.4%) |
Country | ||||||||||
USA | 13 | (56.5%) | 2 | (11.8%) | 6 | (66.7%) | 0 | (0.0%) | 21 | (41.2%) |
UK | 4 | (17.4%) | 2 | (11.8%) | 0 | (0.0%) | 0 | (0.0%) | 6 | (11.8%) |
Canada | 1 | (4.3%) | 2 | (11.8%) | 1 | (11.1%) | 2 | (100.0%) | 6 | (11.8%) |
Other | 5 | (21.7%) | 11 | (64.7%) | 2 | (22.2%) | 0 | (0.0%) | 18 | (35.3%) |
Disease/condition | ||||||||||
Infections and infestations | 4 | (17.4%) | 2 | (11.8%) | 1 | (11.1%) | 0 | (0.0%) | 7 | (13.7%) |
Cardiac disorders | 3 | (13.0%) | 3 | (17.6%) | 1 | (11.1%) | 0 | (0.0%) | 7 | (13.7%) |
Psychiatric disorders | 4 | (17.4%) | 3 | (17.6%) | 0 | (0.0%) | 0 | (0.0%) | 7 | (13.7%) |
Other | 12 | (52.2%) | 9 | (52.9%) | 7 | (77.8%) | 2 | (100.0%) | 30 | (58.8%) |
Primary outcome of study | ||||||||||
Efficacy | 12 | (52.2%) | 16 | (94.1%) | 2 | (22.2%) | 0 | (0.0%) | 30 | (58.8%) |
Safety | 2 | (8.7%) | 1 | (5.9%) | 6 | (66.7%) | 2 | (100.0%) | 11 | (21.6%) |
Efficacy and safety | 9 | (39.1%) | 0 | (0.0%) | 1 | (11.1%) | 0 | (0.0%) | 10 | (19.6%) |
Type of variable (primary outcome) | ||||||||||
Binary | 22 | (95.7%)a | 13 | (76.5%) | 5 | (55.6%) | 1 | (50.0%) | 41 | (80.4%) |
Time to event | 1 | (4.3%) | 4 | (23.5%) | 4 | (44.4%) | 1 | (50.0%) | 10 | (19.6%) |
Relative effect measure | ||||||||||
Yes | ||||||||||
Relative risk | 11 | (47.8%)b | 5 | (29.4%) | 2 | (22.2%) | 0 | (0.0%) | 18 | (35.3%)a |
Odds ratio | 9 | (39.1%)b | 4 | (23.5%) | 2 | (22.2%) | 1 | (50.0%) | 16 | (31.4%)a |
Hazard ratio | 1 | (4.3%) | 3 | (17.6%) | 3 | (33.3%) | 0 | (0.0%) | 7 | (13.7%) |
Rate ratio | 0 | (0.0%) | 0 | (0.0%) | 1 | (11.1%) | 1 | (50.0%) | 2 | (3.9%) |
No | 3 | (13.0%) | 5 | (29.4%) | 1 | (11.1%) | 0 | (0.0%) | 9 | (17.6%) |
Outcome expressed with NNT | ||||||||||
Primary outcome | 6 | (26.1%) | 14 | (82.4%) | 7 | (77.8%) | 1 | (50.0%) | 28 | (54.9%) |
Secondary outcome | 0 | (0.0%) | 2 | (11.8%) | 0 | (0.0%) | 0 | (0.0%) | 2 | (3.9%) |
Primary and secondary outcomes | 17 | (73.9%) | 1 | (5.9%) | 2 | (22.2%) | 1 | (50.0%) | 21 | (41.2%) |
NNT for benefit or harm? | ||||||||||
Benefit | 8 | (34.8%) | 15 | (88.2%) | 3 | (33.3%) | 0 | (0.0%) | 26 | (51.0%) |
Harm | 2 | (8.7%) | 1 | (5.9%) | 6 | (66.7%) | 2 | (100.0%) | 11 | (21.6%) |
Benefit and harm | 13 | (56.5%) | 1 | (5.9%) | 0 | (0.0%) | 0 | (0.0%) | 14 | (27.5%) |
Type of NNT calculated in the study | ||||||||||
Person-based NNT | 21 | (91.3%)a | 13 | (76.5%) | 5 | (55.6%) | 1 | (50.0%) | 40 | (78.4%) |
Person-time-based NNT | 2 | (8.7%) | 4 | (23.5%) | 4 | (44.4%) | 1 | (50.0%) | 10 | (21.6%) |
Completeness of NNT estimate | ||||||||||
Control event rate | ||||||||||
Yes | 13 | (56.5%) | 17 | (100.0%) | 6 | (66.7%) | 1 | (50.0%) | 37 | (72.5%) |
No | 10 | (43.5%) | 0 | (0.0%) | 3 | (33.3%) | 1 | (50.0%) | 14 | (27.5%) |
Time horizon | ||||||||||
Yes | 10 | (43.5%) | 17 | (100.0%) | 9 | (100.0%) | 2 | (100.0%) | 37 | (72.5%) |
No | 13 | (56.5%) | 0 | (0.0%) | 0 | (0.0%) | 0 | (0.0%) | 14 | (27.5%) |
Confidence intervals | ||||||||||
Yes | 16 | (65.2%)c | 8 | (47.1%) | 8 | (88.9%) | 1 | (50.0%) | 32 | (62.7%) |
No | 8 | (34.8%) | 9 | (52.9%) | 1 | (11.1%) | 1 | (50.0%) | 19 | (37.3%) |