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Table 3 Willingness to participate, participation rates, and conditional participation rates in trial 1 and 2

From: Improving participation rates by providing choice of participation mode: two randomized controlled trials

Invitation formats No choice Choice     
TRIAL 1 interview (n = 198) interview or questionnaire (n = 193) X 2 df p RR (95%CI)
Participation rate 130 (66%) 125 (65%) 0.03 1 0.853 0.98 (0.74 - 1.28)
Conditional participation rate 130 (90%) 125 (72%) 15.65 1 <.01 0.37 (0.22 - 0.63)
Willing to participate 145 (73%) 174 (90%) 18.63 1 <.01 2.72 (1.67 - 4.42)
  No choice Choice     
TRIAL 2 questionnaire (n = 294) interview or questionnaire (n = 298) X 2 df p RR (95%CI)
Participation rate 134 (46%) 177 (59%) 11.33 1 <.01 1.34 (1.13 - 1.59)
Conditional participation rate 134 (53%) 177 (66%) 9.25 1 <.01 1.39 (1.12 - 1.71)
Willing to participate 253 (86%) 268 (90%) 2.11 1 0.146 1.39 (0.89 - 2.16)
  1. Abbreviations: X2 = chi square, RR = relative risk.