Table 1

Participation and demographic characteristics of the exposed (South Iceland) and non-exposed (North Iceland) populations

ExposedNon-exposed
% (n/N)% (n/N)p Value
Target population (identified in total population registers)1811751
 Could not be found or reached10.8 (196/1811)7.2 (54/751)0.01
Study population1615697
 Refused to participate17.8 (286/1615)14.6 (102/697)0.07
Originally agreed to participate1329595
 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
 Male49.0 (562)51.4 (262)0.36
 Female51.0 (586)48.6 (248)0.36
Age categories
 18–2311.1 (128/1148)8.2 (42/510)0.07
 24–308.6 (99/1148)9.0 (46/510)0.79
 31–4015.2 (175/1148)14.3 (73/510)0.55
 41–5020.3 (233/1148)21.4 (109/510)0.62
 51–6019.3 (222/1148)22.2 (113/510)0.19
 61–7015.9 (183/1148)16.5 (84/510)0.79
 71–809.4 (108/1148)8.4 (43/510)0.52
Education
 No formal education5.4 (61/1134)4.8 (24/501)0.62
 Primary education35.9 (407/1134)30.9 (155/501)0.05
 Secondary education33.4 (379/1134)37.7 (189/501)0.09
 Professional or university education20.6 (234/1134)23.8 (119/501)0.16
 Other education*4.7 (53/1134)2.8 (14/501)0.08
Marital status
 Married or cohabitating72.4 (831/1148)76.6 (391/510)0.07
 Single or divorced18.3 (210/1148)15.5 (79/510)0.17
 Relationship—no cohabitation6.8 (78/1148)4.7 (24/510)0.10
 Widow or widower2.5 (29/1148)3.1 (16/510)0.48
Household size
 1 adult13.8 (151/1096)15.4 (76/494)0.40
 2 adults51.4 (563/1096)56.1 (277/494)0.40
 3 adults21.3 (233/1096)18.0 (89/494)0.14
 ≥4 adults13.6 (149/1096)10.5 (52/494)0.09
Occupational status
 Full-time job60.4 (683/1130)61.0 (310/507)0.79
 Part-time job9.1 (103/1130)11.6 (59/507)0.11
 Unemployed3.5 (40/1130)1.2 (6/507)0.01
 Student6.9 (78/1130)5.7 (28/507)0.29
 Homemaker or maternity leave9.4 (99/1130)7.8 (40/507)0.56
 Retired6.1 (69/1130)6.3 (32/507)0.87
 On disability or sick leave5.1 (58/1130)6.3 (32/507)0.33
Financial situation
 Very good4.6 (52/1136)4.3 (22/510)0.81
 Good23.9 (271/1136)26.3 (134/510)0.92
 Acceptable (‘making ends meet’)55.6 (632/1136)56.1 (286/510)0.87
 Bad13.5 (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 statusLowMediumHighNon-exposed area
 Never smoker57.2 (87/152)58.5 (377/644)54.0 (190/352)54.3 (277/510)0.31
 Former smoker28.9 (44/152)24.5 (158/644)26.1 (92/352)26.3 (134/510)0.69
 Current smoker13.8 (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.