1. Department of Preventive MedicineSchool of MedicineKyungpook National University Daegu 41944 Korea
2. Division of Epidemiology and Community HealthSchool of Public HealthUniversity of Minnesota Minneapolis Minnesota 55454 USA
3. Department of Medical SciencesCardiovascular EpidemiologyUppsala University Uppsala 75237 Sweden
4. Department of Medical SciencesOccupational and Environmental MedicineUppsala University Uppsala 75185 Sweden