Is the overall SMR a useful measure of mortality in occupational cohort studies?
DOI:
https://doi.org/10.5324/nje.v9i1.447Abstract
Objectives.
Methods.
ptw is presented which is the sum of the stratum specific observed/expected ratios
weighted by the person-time distribution.
Results.
ptw of 1.18 were estimated for this cohort.
Conclusions.
Traditional SMR analyses of occupational cohorts are in general influenced by the distribution
of age and active/inactive person-time. To reduce the influence of random variations in these
distributions it is proposed to perform person-time weighting of the age, employment status, and calendar
time strata. The healthy hire effect and the healthy worker survivor effect (HWSE) are the main
components of the HWE which did not decline by increasing duration of follow-up.
The proportions of person-time attributed from the highest age stratum (≥ 65 years) and theproportions of all inactive person-time varied considerably between the populations from the 12 plants.
Among individuals aged < 65 years the overall SMRs increased by increasing proportions of inactive
person-time. The inactive person-time stratum among individuals aged 65 years or more showed an
SMR close to 1.00. The active person-time SMRs were fairly stable over increasing strata of duration
of follow-up. A traditional SMR of 1.08 and an SMR
A previously defined cohort of 14 730 male workers from 12 Norwegian ferroalloy plants
was studied with analyses of the overall SMR stratified by age at risk, employment status, periods of
observation and duration of follow-up. The age distribution and the proportions of active and inactive
person-time were also examined among workers from each of the 12 plants. An alternative SMR notion
designated SMR
This study was performed to examine the importance of the age structure of a cohort and
the impact of the healthy worker effect (HWE) on the overall standardised mortality ratio (SMR), and
to investigate the components of the HWE.
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