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Table 1 Trial characteristics

From: A systematic review of the “promising zone” design

  Trials included in the review (N = 30)
n/N %
Interim analysis details
 Number of interim analyses planned
 1 28/30 93.3
 2 2/30 6.7
 Timing of the first interim analysis1 (% of initially planned sample size)
 Median (IQR) 60.0 (41.1, 72.6)
 Status of information at the first interim analysis
 Completed data collection (primary outcome) 14/23 60.9
 Recruited 5/23 21.7
 Events occurred 4/23 17.4
 Result at first interim analysis
 Continue 4/13 30.8
 Stop 2/13 15.4
 SSR 7/13 53.8
 Maximum sample size percentage increase2
 Median (IQR) 50.0 (35.3, 100.0)
 Actual sample size percentage increase3
 Median (IQR) 11.56 (1.12, 42.3)
 Stopping boundaries?4
 Yes 15/21 71.4
 If yes, type of stopping boundary
 Efficacy 4/15 26.7
 Futility 5/15 33.3
 Efficacy and futility 4/15 26.7
 Not specified 2/15 13.3
General trial characteristics
 Primary outcome type
 Binary 16/33 48.5
 Continuous 10/33 30.3
 Time-to-event 7/33 21.2
 Time to primary outcome
 0–3 days 5/30 16.7
 1–6 weeks 6/30 20.0
 8–12 weeks 6/30 20.0
 5–6 months 4/30 13.3
 1–5 years 9/30 30.0
 Number of groups
 2 29/30 96.7
 4 1/30 3.3
 Study design
 Cluster 1/30 3.3
 Crossover 1/30 3.3
 Parallel group 28/30 93.3
 Phase6
 I 1/20 5.0
 II 6/20 30.0
 III 13/20 65.0
 Disease area
 Cardiovascular 5/30 16.7
 Diabetes 4/30 13.3
 Neurology 7/30 23.3
 Oncology 5/30 16.7
 GI 2/30 6.7
 Others**** 7/30 23.3
 Progress
 In progress 12/30 40.0
 In analysis 3/30 10.0
 Completed 15/30 50.0
 Funder type
 Industry 17/30 56.7
 Non-industry 13/30 43.3
  1. 1No timing of interim look data from 3 trials
  2. 2No maximum sample size reported for 9 trials
  3. 3Based on the 12 trials that implemented a SSRE
  4. 4No information on usage of stopping boundaries for 9 trials
  5. 5Three trials had > 1 primary outcome: continuous and binary (n = 1), binary and time-to-event (n = 1) and two time-to-event (n = 1)
  6. 6Other disease areas include one trial each in critical care, emergency medicine, haematology, dental care, orthopaedic, ostomy and pain