The procedures adopted for cohort enumeration, follow-up, vital status ascertainment and causes of death coding complied with recommended standards in occupational epidemiology [ 19].
The overall incidence rate of IID presenting to general practice will be calculated from the total number of cases reported in the GP Presentation Study, adjusted for under-ascertainment, and in the Enumeration Study, and the follow-up time of all persons registered in the practice populations.
Other important cost determinants include method of ascertainment (such as registry vs. household enumeration), complexity of data collection, and follow-up methods (such as active vs. passive).
That we did not encounter refusals in this study may be because households reporting chronic coughers had, at the enumeration phase, been informed about possible follow-up visits by a qualitative research team.
Obviously, verification of this statement would require studies in which large numbers of patients are included with enumeration of CEC at baseline and during follow-up.
OS was calculated from the date of baseline CTC enumeration to the date of death or last follow-up.
The original cohort included the enumeration area of residence in 1991 and mortality follow-up through 2001.
The observation that advanced cancer patients have higher CEC counts than healthy controls (Beerepoot et al, 2004; Rowand et al, 2007), whereas patients with stable disease and healthy individuals have similar numbers (Beerepoot et al, 2004), may imply that CEC enumeration may be used for prognosis and during follow-up in cancer patients.
The main strengths of this study lie in its prospective design, the completeness of the enumeration of the cohort, and the high success rate in follow-up.
The surveillance is designed as an open cohort of individuals who enter through initial census enumeration, birth, and in-migration and exit through out-migration, lost to follow-up, and death.
The NLMS is an on-going mortality follow-up study of selected cohorts of CPS respondents and the 1980 E sample (a post-enumeration sample used to measure the undercount of the 1980 Decennial Census).
