Table 1 Characteristics of participants
| Â | February | May | July | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Â | Kumamoto | Niigata | Kumamoto | Niigata | Kumamoto | Niigata | ||||||
N | 1537 | 1350 | 1101 | 1119 | 905 | 987 | ||||||
| Â | 100% | 100% | 71.6% v. Feb | 82.9% v. Feb | 58.9% v. Feb | 73.1% v. Feb | ||||||
Year of survey | N | Â | N | Â | N | v. Feb | N | v. Feb | N | v. Feb | N | v. Feb |
 2010 | 186 | 12.1% | – | – | 121 | 65.1% | – | – | 104 | 55.9% | – | – |
 2011 | 212 | 13.8% | 198 | 14.7% | 159 | 75.0% | 152 | 76.8% | 140 | 66.0% | 132 | 66.7% |
 2012 | 306 | 19.9% | 299 | 22.1% | 234 | 76.5% | 225 | 75.3% | 196 | 64.1% | 192 | 64.2% |
 2013 | 287 | 18.7% | 243 | 18.0% | 197 | 68.6% | 212 | 87.2% | 163 | 56.8% | 191 | 78.6% |
 2014 | 274 | 17.8% | 305 | 22.6% | 202 | 73.7% | 266 | 87.2% | 155 | 56.6% | 230 | 75.4% |
 2015 | 272 | 17.7% | 305 | 22.6% | 188 | 69.1% | 264 | 86.6% | 147 | 54.0% | 242 | 79.3% |
Age | ||||||||||||
 years old (mean ± SD) | 64.4 ± 9.8 | 59.1 ± 6.2 | 65.9 ± 9.5 | 59.5 ± 6.1 | 66.7 ± 9.5 | 59.7 ± 6.1 | ||||||
Gender | N | Â | N | Â | N | Â | N | Â | N | Â | N | Â |
 Male | 1089 | 70.9% | 939 | 69.6% | 798 | 72.5% | 771 | 68.9% | 663 | 73.3% | 674 | 68.3% |
 Female | 448 | 29.2% | 411 | 30.4% | 303 | 27.5% | 348 | 31.1% | 242 | 26.7% | 313 | 31.7% |
Body mass index | ||||||||||||
 kg/m2 (mean ± SD) | 23.6 ± 3.1 | 23.2 ± 3.1 | 23.4 ± 2.9 | 23.1 ± 3.0 | 23.3 ± 2.9 | 23.0 ± 3.0 | ||||||
Smoking status | N | Â | N | Â | N | Â | N | Â | N | Â | N | Â |
 Current smoker | 210 | 13.7% | 312 | 23.1% | 121 | 11.0% | 232 | 20.7% | 89 | 9.8% | 192 | 19.5% |
 Former smoker | 561 | 36.5% | 481 | 35.6% | 430 | 39.1% | 422 | 37.7% | 364 | 40.2% | 367 | 37.2% |
 Never smoker | 766 | 49.8% | 557 | 41.3% | 550 | 50.0% | 465 | 41.6% | 452 | 49.9% | 428 | 43.4% |
Working status | N | Â | N | Â | N | Â | N | Â | N | Â | N | Â |
 Active worker | 951 | 63.6% | 1169 | 86.9% | 608 | 56.1% | 939 | 84.1% | 463 | 52.0% | 820 | 83.3% |
 Retired/ Not in employment | 544 | 36.4% | 177 | 13.2% | 476 | 43.9% | 178 | 15.9% | 428 | 48.0% | 165 | 16.8% |
Time spent outdoors | ||||||||||||
 Hours | 4.0 ± 3.2 | 4.7 ± 4.2 | 4.2 ± 3.2 | 4.1 ± 3.6 | 4.0 ± 3.1 | 3.9 ± 3.4 | ||||||
Prevalence of respiratory symptoms | ||||||||||||
 1. Weather affects cough | 88 | 5.8% | 86 | 6.4% | 76 | 7.1% | 66 | 6.0% | 37 | 4.2% | 59 | 6.1% |
 2. Sputum production without a cold | 391 | 25.5% | 397 | 29.5% | 303 | 28.4% | 320 | 28.9% | 222 | 25.0% | 253 | 26.0% |
 3. Sputum production in early morning | 258 | 16.9% | 213 | 15.8% | 193 | 18.1% | 172 | 15.6% | 142 | 16.0% | 160 | 16.6% |
 4. Frequent wheezes | 123 | 8.0% | 108 | 8.0% | 89 | 8.3% | 91 | 8.3% | 54 | 6.1% | 70 | 7.2% |
 5. Allergy | 307 | 20.0% | 232 | 17.3% | 239 | 22.1% | 239 | 21.6% | 145 | 16.3% | 164 | 16.9% |
Monitoring station | ||||||||||||
 Number of stations | 26 | 23 |  |  |  |  |  |  |  |  | ||
Distance from each residence | ||||||||||||
 Median (Min. – Max.) (km) | 3.70 (0.06–33.43) | 3.31 (0.10–30.88) |  |  |  |  |  |  |  |  | ||