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Table 2 Assessment of methodology used to calculate number needed to treat (NNT) in included studies

From: Number needed to treat (NNT) in clinical literature: an appraisal

  Meta-analysis (n = 23) RCT (n = 17) Cohort (n = 9) Nested case–control (n = 2) Overall (n = 51)
Methodology used to calculate NNT is defined in the methods section of the study
 Yes 19 82.6%) 0 (0.0%) 7 (77.8%) 2 (100.0%) 28 (54.9%)
 No 4 17.4%) 17 (100.0%) 2 (22.2%) 0 (0.0%) 23 (45.1%)
General characteristics of the methodology used to calculate NNT in the study
 Reciprocal of risk difference
  Simple proportions 1 (4.3%) 14 (82.4%) 2 (22.2%) 0 (0.0%) 17 (33.3%)
  Cumulative IR 0 (0.0%) 3 (17.6%) 3 (33.3%) 0 (0.0%) 6 (11.8%)
  Pooled RD 12 (52.2%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 12 (23.15)
  Average RD 0 (0.0%) 0 (0.0%) 4 (44.4%) 0 (0.0%) 4 (7.8%)
 Relative effect measure 10 (43.5%) 0 (0.0%) 0 (0.0%) 2 (100.0%) 12 (23.5%)
Methodology used to calculate NNT is in line with basic recommendations (overall)
 Yes 10 (43.5%) 16 (94.1%) 8 (88.9%) 2 (100.0%) 37 (70.6%)
 No 13 (56.5%) 1 (5.9%) 1 (11.1%) 0 (0.0%) 15 (29.4%)
Methodology used to calculate NNT is in line with basic recommendations (detailed)
 Binary variables
  Yes 9 (39.1%) 13 (76.5%) 5 (55.6%) 1 (50.0%) 28 (54.9%)
 Reciprocal of risk difference
  Simple proportions 0 (0.0%) 13 (76.5%) 1 (11.1%) 0 (0.0%) 14 (27.5%)
  Cumulative IR 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%)
  Pooled RD 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%)
  Average RD 0 (0.0%) 0 (0.0%) 4 (44.4%) 0 (0.0%) 4 (7.8%)
  Relative effect measure 9 (39.1%) 0 (0.0%) 0 (0.0%) 1 (50.0%) 10 (19.6%)
 No 13 (56.5%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 13 (25.5%)
 Reciprocal of risk difference
  Simple proportions 1 (4.3%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 1 (2.0%)
  Cumulative IR 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%)
  Pooled RD 12 (52.2%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 12 (23.5%)
  Average RD 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%)
 Relative effect measure 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%)
 Time-to-event variables
  Yes 1 (4.3%) 3 (17.6%) 3 (33.3%) 1 (50.0%) 8 (15.7%)
 Reciprocal of risk difference
  Simple proportions 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%)
  Cumulative IR 0 (0.0%) 3 (17.6%) 3 (33.3%) 0 (0.0%) 6 (11.8%)
  Pooled RD 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%)
  Average RD 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%)
 Relative effect measure 1 (4.3%) 0 (0.0%) 0 (0.0%) 1 (50.0%) 2 (3.9%)
 No 0 (0.0%) 1 (5.9%) 1 (11.1%) 0 (0.0%) 2 (3.9%)
  Reciprocal of risk difference
  Simple proportions 0 (0.0%) 1 (5.9%) 1 (11.1%) 0 (0.0%) 2 (3.9%)
  Cumulative IR 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%)
  Pooled RD 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%)
  Average RD 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%)
  Relative effect measure 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%)
  1. IR incidence rate, RCT randomized controlled trial, RD risk difference