Table 6

Association between the trial retention rate (% of randomised participants with valid primary outcome data for analysis) and trial characteristics

CharacteristicnMedianIQRp Value
Setting
 Hospital8192.481.7–99.1 
 General practice2085.677.4–91.0 
 Mixed2590.084.8–97.4 
 Community1685.479.1–96.10.019*†
 Other899.498.8–100.0 
Arms
 21000.900.82–0.98 
 3300.890.79–0.97 
 4+200.920.83–0.970.747†
Control type
 Placebo3090.088.7–99.4 
 Active12089.981.0–97.40.166‡
Final target recruitment
 ≤2001793.787.6–98.3 
 201–4004989.279.8–96.8<0.001§
 401–6002786.772.2–100.0 
 601–8001386.383.2–89.9 
 >8004494.076.4, 99.4 
Total recruitment
 ≤2002394.786.4–100.0 
 201–4004889.179.3–96.4<0.001§
 401–6002885.781.7–92.5 
 601–8001289.988.5–94.6 
 >8003994.077.8–99.3 
Timing of final follow-up
 <1 month999.377.4–100.0 
 1–6 months4194.684.8–100.00.693§
 6–18 months6286.275.1–96.8 
 >18 months3389.285.6–95.4 
  • *The category ‘other’ was not included in Kruskal-Wallis test.

  • †p Values are reported from a Kruskal-Wallis test.

  • ‡p Values are reported from a Wilcoxon rank sum test.

  • §p Values are reported from a nonparametric test of trend (Cuzick).