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Table 1 Response to Invitation and Participation in the Bremen Study Center of the German National Cohort

From: Study invitations with envelopes made from recycled paper do not increase likelihood of active responses or study participation in the German National Cohort

  Active response (N = 3518) Participation (N = 3447d)
No Yesa ORb (95% CI) No Yes ORc (95% CI)
n % n % n % n %
Envelope color
 White 1929 95.4 93 4.6 1 1766 89.0 218 11.0 1
 Grey 1418 94.8 78 5.2 1.16 (0.83, 1.62) 1308 89.4 155 10.6 0.95 (0.76, 1.19)
Sexe
 Female 1108 93.8 73 6.2 1 1003 86.2 161 13.8 1
 Male 2239 95.8 98 4.2 0.73 (0.53, 1.02) 2071 90.7 212 9.3 0.71 (0.57, 0.90)
Nationalitye
 Non-German 690 98.6 10 1.4 1 644 96.4 24 3.6 1
 German 2657 94.3 161 5.7 3.75 (2.07, 7.66) 2430 87.4 349 12.6 3.46 (2.31, 5.43)
Age
 20–29 339 96.0 14 4.0 1.41 (0.73, 2.56) 319 93.3 23 6.7 0.89 (0.54, 1.41)
 30–39 182 96.8 6 3.2 1.15 (0.43, 2.57) 177 95.7 8 4.3 0.58 (0.26, 1.15)
 40–49 1321 96.9 43 3.2 1 1233 91.9 109 8.1 1
 50–59 887 94.1 56 5.9 1.78 (1.19, 2.69) 784 85.0 138 15.0 1.83 (1.40, 2.40)
 60–69 618 92.2 52 7.8 2.25 (1.48, 3.43) 561 85.5 95 14.5 1.67 (1.24, 2.25)
N 3347   171    3074   373   
  1. OR odds ratio, CI confidence interval
  2. aIncludes subjects who replied by letter, phone call, e-mail or visited the study center in person
  3. bAdjusted for pre-trial likelihood of active responses to invitation letter stratified by weekdays
  4. cAdjusted for pre-trial study participation stratified by weekdays
  5. dSubjects excluded from analysis (N = 71): recruitment not complete (N = 22), subject not eligible, not capable, or deceased (N = 49)
  6. eInformation provided by Bremen’s resident registration office