Table 3

Effects of interventions to improve recruitment

Intervention Reference IDParticipants recruitedRisk ratio (95% CI)Absolute difference (%)*HeterogeneityRisk of bias† (studies)
InterventionComparatorχ2p ValueI2 (%)
Trial design
 Open vs blind design16 321161/23391029/24941.22 (1.09 to 1.36)92.740.1064A│A (2)
 Active comparator vs placebo5965/21885/2180.76 (0.59 to 0.99)−9C (1)
 Patient preference vs conventional RCT1890/13597/1380.95 (0.81 to 1.11)−4A (1)
Obtaining consent
Consent process Opt-out vs opt-in5540/6044/921.39 (1.06 to 1.84)19A (1)
 Consent to experimental vs usual48‡, 501087/1320920/11361.01 (0.98 to 1.05)10.420.510B│C (2)
 Consent to standard vs usual48‡, 50325/623920/11360.76 (0.49 to 1.17)−1914.74<0.00193B│C (2)
 Refusers choose treatment vs usual50482/607836/9850.94 (0.89 to 0.98)−5C (1)
 Physician modified consent vs usual4891/15084/1511.09 (0.90 to 1.32)5B (1)
 Participant modified consent vs usual4885/15084/1511.02 (0.83 to 1.24)1B (1)
Consent form Researcher read vs participant read5627/5125/531.12 (0.76 to 1.65)6C (1)
Approach to participants
Delivery of information Full video presentation+Q&A vs standard info+brief video+Q&A3564/9366/950.99 (0.82 to 1.20)−1B (1)
 Video presentation+written information vs written only6026/4217/481.75 (1.11 to 2.74)26B (1)
 Audiovisual information on trials vs standard21 22 3388/24782/2481.20 (0.75 to 1.91)74.000.1450B│C│A (3)
 Interactive computer presentation vs paper-based information3623/3017/301.35 (0.93 to 1.96)20C (1)
 Interactive computer presentation vs audio-taped information4431/5021/501.48 (1.00 to 2.18)20B (1)
 Verbal educational session+information brochure vs brochure only45178/232147/2181.14 (1.01 to 1.28)9C (1)
Supplementing information Booklet on trials+standard information vs standard information only23‡, 3427/5325/571.18 (0.64 to 2.18)82.380.1258C│C (2)
 Study questionnaire with invitation vs invitation only31 37333/1483281/14701.14 (0.77 to 1.64)§34.410.0477A│A (2)
 Newspaper article+study information vs study information only5173/224371/22451.03 (0.75 to 1.42)0B (1)
 Favourable article+information vs standard article+information5157/137454/13711.05 (0.73 to 1.52)0B (1)
Framing and content Treatment described as working ‘twice as fast’ vs ‘half as fast’5235/5220/481.62 (1.10 to 2.37)26B (1)
 Trial of treatment described as new vs treatment described as standard3843/6450/600.81 (0.66 to 0.99)−16C (1)
 Information emphasising pain involved vs standard information5418/5130/470.55 (0.36 to 0.85)−29B (1)
 Information emphasising risk involved vs standard information5413/5030/470.41 (0.24 to 0.68)−38B (1)
 Negative framing vs neutral framing of side-effects/survival4320/3023/300.87 (0.63 to 1.20)−10B (1)
 Positive framing vs neutral framing of side-effects/survival4318/3023/300.78 (0.55 to 1.11)−17B (1)
 Total information disclosure vs standard disclosure5327/2923/281.13 (0.93 to 1.38)11A (1)
 Less detailed information on risk and benefits vs more detailed information274/103/91.20 (0.36 to 3.97)7B (1)
 Information leaflet+verbal explanation vs information leaflet only2710/187/191.51 (0.73 to 3.10)19B (1)
Telephone contact Telephone reminder vs no reminder31 49165/536117/5221.66 (1.03 to 2.46)§152.440.1259A│A (2)
 SMS messages (inc quotes) vs no SMS messages2617/4050/40635.09 (2.12 to 581.48)4A (1)
Eligibility screening Enhanced recruitment (inc African American interviewer) vs standard2478/307995/32970.88 (0.65 to 1.18)0B (1)
 Enhanced recruitment+baseline data by telephone vs standard2487/307595/32970.98 (0.74 to 1.31)0B (1)
 Enhanced recruitment+baseline data face-to-face vs standard24116/294995/32971.37 (1.05 to 1.78)1B (1)
 Researcher-administered screening questionnaire vs standard paper based2942/7876/1411.00 (0.77 to 1.29)0C (1)
 Electronic screening questionnaire vs standard paper based2969/15176/1410.85 (0.67 to 1.07)−8C (1)
 Telephone screening vs face-to-face screening2064/99190/3701.26 (1.06 to 1.50)13C (1)
 Eligibility screening by senior investigator vs screening by research assistant4628/16222/1851.45 (0.87 to 2.44)5C (1)
Financial incentives
 Cash incentive+study information vs information only2613/2461/24512.95 (1.71 to 98.21)5A (1)
  • ‡Recruitment to a hypothetical trial.

  • *Absolute difference between the intervention and comparator groups (for multistudy interventions, this was calculated using the risk ratio and average comparator group risk).

  • †Risk of bias: A, low; B, moderate; C, high.

  • §Analysed as an OR and converted to a risk ratio using the average comparator group risk.