Some medical record was obtained for 72% of the decedents, but only 45% of the decedents had medical records with adequate information to determine lifetime cancer incidence.
A decedent was allowed in the analysis if either the next of kin reported his cancer history or adequate medical record data were available. However, a larynx cancer reported by next of kin had to be confirmed by medical record to be accepted into the analysis.
Live individuals were admitted for analysis only if they had filled out a questionnaire or were interviewed by phone. No larynx cancers were accepted unless confirmed by a physician.
Altogether, 77% (n = 879) of the original cohort met these criteria and were eligible for the analysis of larynx cancer incidence. These men contributed over 27,000 person-years-at-risk of larynx cancer, with person-years-at-risk beginning at date of first exposure for each man (date of first working in pickling) and continuing until the date last observed (end of follow-up). For people who did not die and were successfully traced, the date last observed generally was sometime in 1986. For people who died, the date last observed was their date of death.
After considering the above, try and answer the following questions: