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Table 3 Self-selection bias analysis comparing the number and proportion of respondents from each study region and residential air pollution exposures for web survey respondents vs. mail survey respondents

From: Self-reported data in environmental health studies: mail vs. web-based surveys

 Web survey respondentsMail survey respondentsp-value
Region a0.185 c
 Anholt7 (2)15 (2)
 Keldsnor10 (4)51 (6)
 Lindet46 (17)155 (20)
 Sundeved212 (77)570 (72)
Residential exposure b
 NO2 (μg/m3)4.41 ± 0.534.42 ± 0.560.652 d
 PM2.5 (μg/m3)10.92 ± 0.3110.94 ± 0.270.466 d
 NH3 (μg/m3)2.34 ± 0.862.28 ± 1.010.310 d
  1. a Number of individuals (percentage)
  2. b Mean ± standard deviation
  3. c Pearson’s Chi-squared test of proportions
  4. d Two sample t-test