NIOSH has recently completed development on a personal computer version of its life table analysis program (PC LTAS, Version 1.0). The PC LTAS is analogous to the mainframe version of NIOSH LTAS [Steenland et al., 1990], although it includes some new features and has more flexibility. NIOSH PC LTAS uses demographic and work history data to calculate person-time at risk and corresponding mortality (or incidence) rates for an exposed population. Person-time for each individual either begins at first expo- sure, or at a user-specified calendar date, or at a user- specified date specific to each subject in the study. Person- time may end as a common user-specified date for all subjects, or at a user-specified subject-specific date for each subject Calculated rates for the cohort under study are stratified by age (5-year categories), calendar time (5-year categories), race (white/nonwhite), and gender before being compared to rates for a nonexposed population. Rates for several nonexposed populations are provided with the program and are also appropriately stratified by age, calendar time, race, and gender. PC LTAS calculates standardized mortality ratios (SMRs) comparing exposed to nonexposed rates for a large number of causes of death (or disease), as well as the associated confidence limits based on a Poisson distribution. SMRs are also calculated separately by user- specified categories of either duration of exposure or cumulative exposure (up to 30 categories). In addition, directly standardized rate ratios (SRRs) may be calculated when requested, as well as associated tests for the trend across duration or cumulative exposure categories for the directly standardized rate ratios.
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