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
| Â | Web survey respondents | Mail survey respondents | p-value |
|---|---|---|---|
Region a | 0.185 c | ||
 Anholt | 7 (2) | 15 (2) | |
 Keldsnor | 10 (4) | 51 (6) | |
 Lindet | 46 (17) | 155 (20) | |
 Sundeved | 212 (77) | 570 (72) | |
Residential exposure b | |||
 NO2 (μg/m3) | 4.41 ± 0.53 | 4.42 ± 0.56 | 0.652 d |
 PM2.5 (μg/m3) | 10.92 ± 0.31 | 10.94 ± 0.27 | 0.466 d |
 NH3 (μg/m3) | 2.34 ± 0.86 | 2.28 ± 1.01 | 0.310 d |