Symptom prevalence of the diary panel sub-cohort, by zone and year (n = 380)a.

aEach subject contributed up to 63 days of data in the diary study.bParticipants in overlapping area of increased exposure zone and stack zone, diary panel cohort (2006 = 6(4); 2007 = 5(2); 2008 = 5(3)), contributed data to both zones. n = subjects in overlapping area with spirometry; (n) = subjects in overlapping area taking part in peak flow and symptom diary.cPanel sub-cohort participants who took part in peak flow/symptom diary.dSymptoms recorded by diary. % represents proportion of subjects experiencing those symptoms a) at least one day during the study period; b) >10% of days during the study period; c) >20% of days during the study period.eComposite variables derived from variables measured in questionnaire (See Table S1, Supporting Information).fAttributes measured by questionnaire.