Table 1.
Participation and demographic characteristics of the exposed (South Iceland) and non-exposed (North Iceland) populations
| Exposed | Non-exposed | ||||
|---|---|---|---|---|---|
| % (n/N) |
% (n/N) | p Value | |||
| Target population (identified in total population registers) | 1811 | 751 | |||
| Could not be found or reached | 10.8 (196/1811) | 7.2 (54/751) | 0.01 | ||
| Study population | 1615 | 697 | |||
| Refused to participate | 17.8 (286/1615) | 14.6 (102/697) | 0.07 | ||
| Originally agreed to participate | 1329 | 595 | |||
| Explained non-participation* | 7.0 (93/1329) | 6.1 (36/595) | 0.44 | ||
| Unexplained non-participation† | 6.6 (88/1329) | 8.2 (49/595) | 0.20 | ||
| Response rate (participants/study population) | 71 (1148/1615) | 73 (510/697) | 0.31 | ||
| Demographic characteristics | |||||
| Male | 49.0 (562) | 51.4 (262) | 0.36 | ||
| Female | 51.0 (586) | 48.6 (248) | 0.36 | ||
| Age categories | |||||
| 18–23 | 11.1 (128/1148) | 8.2 (42/510) | 0.07 | ||
| 24–30 | 8.6 (99/1148) | 9.0 (46/510) | 0.79 | ||
| 31–40 | 15.2 (175/1148) | 14.3 (73/510) | 0.55 | ||
| 41–50 | 20.3 (233/1148) | 21.4 (109/510) | 0.62 | ||
| 51–60 | 19.3 (222/1148) | 22.2 (113/510) | 0.19 | ||
| 61–70 | 15.9 (183/1148) | 16.5 (84/510) | 0.79 | ||
| 71–80 | 9.4 (108/1148) | 8.4 (43/510) | 0.52 | ||
| Education | |||||
| No formal education | 5.4 (61/1134) | 4.8 (24/501) | 0.62 | ||
| Primary education | 35.9 (407/1134) | 30.9 (155/501) | 0.05 | ||
| Secondary education | 33.4 (379/1134) | 37.7 (189/501) | 0.09 | ||
| Professional or university education | 20.6 (234/1134) | 23.8 (119/501) | 0.16 | ||
| Other education* | 4.7 (53/1134) | 2.8 (14/501) | 0.08 | ||
| Marital status | |||||
| Married or cohabitating | 72.4 (831/1148) | 76.6 (391/510) | 0.07 | ||
| Single or divorced | 18.3 (210/1148) | 15.5 (79/510) | 0.17 | ||
| Relationship—no cohabitation | 6.8 (78/1148) | 4.7 (24/510) | 0.10 | ||
| Widow or widower | 2.5 (29/1148) | 3.1 (16/510) | 0.48 | ||
| Household size | |||||
| 1 adult | 13.8 (151/1096) | 15.4 (76/494) | 0.40 | ||
| 2 adults | 51.4 (563/1096) | 56.1 (277/494) | 0.40 | ||
| 3 adults | 21.3 (233/1096) | 18.0 (89/494) | 0.14 | ||
| ≥4 adults | 13.6 (149/1096) | 10.5 (52/494) | 0.09 | ||
| Occupational status | |||||
| Full-time job | 60.4 (683/1130) | 61.0 (310/507) | 0.79 | ||
| Part-time job | 9.1 (103/1130) | 11.6 (59/507) | 0.11 | ||
| Unemployed | 3.5 (40/1130) | 1.2 (6/507) | 0.01 | ||
| Student | 6.9 (78/1130) | 5.7 (28/507) | 0.29 | ||
| Homemaker or maternity leave | 9.4 (99/1130) | 7.8 (40/507) | 0.56 | ||
| Retired | 6.1 (69/1130) | 6.3 (32/507) | 0.87 | ||
| On disability or sick leave | 5.1 (58/1130) | 6.3 (32/507) | 0.33 | ||
| Financial situation | |||||
| Very good | 4.6 (52/1136) | 4.3 (22/510) | 0.81 | ||
| Good | 23.9 (271/1136) | 26.3 (134/510) | 0.92 | ||
| Acceptable (‘making ends meet’) | 55.6 (632/1136) | 56.1 (286/510) | 0.87 | ||
| Bad | 13.5 (153/1136) | 12.0 (61/510) | 0.40 | ||
| Very bad (‘indebted or bankruptcy’) | 2.5 (28/1136) | 1.4 (7/510) | 0.16 | ||
|
Exposure areas‡ |
|||||
| Smoking status | Low | Medium | High | Non-exposed area | |
| Never smoker | 57.2 (87/152) | 58.5 (377/644) | 54.0 (190/352) | 54.3 (277/510) | 0.31 |
| Former smoker | 28.9 (44/152) | 24.5 (158/644) | 26.1 (92/352) | 26.3 (134/510) | 0.69 |
| Current smoker | 13.8 (21/152) | 16.9 (109/644) | 19.9 (70/352) | 19.4 (99/510) | 0.33 |
*Dropped out because of the nature of the questions, because they did not think the study applied to them, or because of illness or old age.
†Did not reply, could not be reached for reminders, did not respond to reminders or returned empty questionnaires.
‡The exposed area was divided into three areas by levels of exposure with regard to magnitude of ash fall, see figure 1. The p value is based on comparison between the non-exposed and the sum of the exposed area.