Table 1.
Basic sociodemographic characteristics (relative frequencies presented as percentages or median with interquartile ranges.
| All Subjects n = 5488 |
Randomized n = 1167 |
Self-Selected n = 4321 |
p | ||
|---|---|---|---|---|---|
| Quantitative variables (median and IQR) | |||||
| Age | Median (IQR) | 44 (32–57) | 48 (34–63) | 43 (31–55) | <0.001 |
| Body mass index | Median (IQR) | 25.2 (22.3–28.7) | 25.6 (22.5–29.0) | 25.2 (22.2–28.5) | 0.08 |
| Missing | 6.7% | 9.8% | 5.9% | ||
| Categorical variables (percentages) | |||||
| Town | Gliwice | 32.5 | 33.6 | 32.2 | 0.7 |
| Katowice | 34.2 | 33.8 | 34.3 | ||
| Sosnowiec | 33.3 | 32.6 | 33.5 | ||
| Gender | Female | 58.3 | 51.3 | 60.1 | <0.001 |
| Male | 41.7 | 48.7 | 39.9 | ||
| Professional activity | Has no job | 31.2 | 43.9 | 27.7 | <0.001 |
| Has a job | 67.6 | 55.5 | 70.9 | ||
| Works and studies | 1.2 | 0.6 | 1.4 | ||
| Month of serological examination | 10/2020 | 9.1 | 38.2 | 1.3 | <0.001 |
| 11/2020 | 74.0 | 60.1 | 77.7 | ||
| 12/2020 | 16.9 | 1.7 | 21.0 | ||
| Vaccinated against tuberculosis | Yes | 76.2 | 68.7 | 78.2 | <0.001 |
| Vaccinated against seasonal influenza last year | Yes | 16.5 | 12.2 | 17.6 | <0.001 |
| Medical help following symptoms | Yes | 21.6 | 19.5 | 22.2 | 0.2 |
| Missing | 2.5 | 3.5 | 2.2 | ||
| Contact with a confirmed case of COVID-19 | Yes | 28.7 | 12.8 | 33.0 | <0.001 |
| Had a post contact test | Yes | 16.6 | 13.0 | 17.5 | 0.001 |
Legend: n—number of participants; p—p-value; IQR—interquartile range; IgG—immunoglobulin G; IgM—immunoglobulin M.