British journal of industrial medicine
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Estimation of exposure-response relations from epidemiological data is complicated by the fact that exposures usually vary in intensity over time. Cumulative exposure indices, which do not separate the effects of intensity and duration, are commonly used to circumvent this problem. In this paper the estimation of relative risk for specific ranges of exposure intensity from such data is considered using existing statistical methods for fitting multivariate relative risk models. ⋯ It also throws light on the possible existence of a threshold. The procedure was applied to data from a cohort of 406 vermiculite miners to examine the lung cancer risk associated with exposure to fibrous tremolite, which contaminated the vermiculite. The pattern of exposure-response differed substantially from that obtained using a cumulative exposure index to assess risk.
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In 1979 all former workers from the Wittenoom asbestos industry who could be traced to an address were sent a questionnaire to determine smoking history. Occupational exposure to crocidolite was known from employment records. Of 2928 questionnaires sent, satisfactory replies were received from 2400 men and 149 women. ⋯ The incidence of both lung cancer and asbestosis was greatest in those subjects with the highest levels of exposure to crocidolite and in ex-smokers. Statistical modelling of the joint effects of these exposures on the incidence of each disease indicated that crocidolite exposure multiplied the rates of lung cancer due to smoking and that smoking has no measurable effect on the rates of asbestosis. There was also some evidence that the incidence rate of lung cancer is falling with time.
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Follow up data on 37,355 employees of the United Kingdom Atomic Energy Authority (UKAEA) for the period 1946-79 were analysed to investigate the extent to which selection for work on the basis of health affected subsequent death rates. Causes of death were grouped into two broad categories for analysis: all cancers and all other causes of death. Evidence for an effect of selection of healthy individuals into the workforce was sought primarily by examining standardised mortality ratios (SMRs) by period since recruitment. ⋯ Apart from this initial fall, there was little evidence of a systematic increase or decrease in mortality with increasing period was not significantly associated with durationof employment for either cause of death category either before or after adjustment for confounding factors. Whereas selection of individuals into or out of the workforce on the basis of health affects the way in which death rates change with time, other factors such as sociodemographic characteristics or health related behaviour determine the general level of mortality in the longer run. The persistently low SMRs observed in this workforce throughout the follow up period suggest that selection on the latter factors are likely to have had a considerable effect on death rates in the UKAEA workforce.
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A retrospective study was carried out on medical evacuations from the installations of four major oil or gas producing companies, or both, operating offshore on the United Kingdom continental shelf. The study covered 1976-84 during which 2162 evacuations were recorded. Of these, 137 (7.7%) required the use of a chartered helicopter. ⋯ As the age of the evacuee increased the proportion of evacuations for injury decreased and that for illness increased. The mean age for evacuation for injury was 28.3 years and for illness 34.4 years. Few evacuations were required for those aged over 45.