<qa>  What is the expected proportion of cases with no evidence of malignancy?We will derive descriptive statistics prevalence of malignancy, sensitivity, specificity, and false negative rates. The overall sample size will be 500 patients who had PTNB of a lung mass within the study period. Approximately 80 are expected to have a biopsy result showing no evidence of malignancy, based on a retrospective review performed under an IRB exemption 87-04, letter dated 92804. The expected proportion of cases with no evidence of malignancy is approximately 0.15. For a 95 confidence interval of 0.15-0.075 we will need follow-up information from 61 patients, considering that this is a descriptive study with a dichotomous variable. This gives us a margin for patients who will be lost to follow-up 