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1.  Low mortality rates in industrial cohort studies due to selection for work and survival in the industry. 
Occupational groups are often described as being relatively healthy because their mortality rates are lower than those of the national average. Although correct this confuses the issue for those who are interested in assessing the effects of exposure to a particular chemical. In a further analysis of data collected in a study of all men ever exposed to vinyl chloride monomer in the manufacture of polyvinyl chloride in Great Britain, three factors have been shown to contribute to the low mortality rates that were observed. The three factors: the selection of a healthy population for employment, the survival in the industry of the healthier men, and the length of time that this population has been pursued, have been quantified. The mortality experience within five years of entering this industry was shown to be as low as 37% of that expected; for circulatory disease and respiratory disease it was as low as 21%. There was a progressive increase in standardized mortality ratio with the length of time since entry so that the effect had almost disappeared 15 years after entry. To avoid confounding the selection effect with the survival effect the latter was measured by separating men who survived 15 years after entering the industry according to whether or not they were still in the industry after this period. Those who had left experienced an overall standardized mortality ratio some 50% higher than those still in the industry. This effect, although consistent in the age groups between 25 and 74 years and for all cause groups studied, was greatest in those aged between 25 and 44 years and for lung cancer and respiratory disease.
PMCID: PMC478970  PMID: 1009272
2.  A survey of occupational cancer in the rubber and cablemaking industries: analysis of deaths occurring in 1972-74. 
The records of 40 867 men employed for at least one year in the rubber and cablemaking industries have now been observed for eight years. This analysis compares the mortality pattern for 1972-74 with that previously reported for 1968-71. It indicates a significant excess of deaths due to cancer of the bladder throughout the industry including men who had not been exposed to acknowledged bladder carcinogens. This excess is in deaths occurring in 1973 and 1974 in the 45-64 and 65 years plus age groups. The two sectors of the industry where this excess is significant are footwear and footwear supplies except adhesives, and the tyre sector. The excess of all cancers taken together previously noted throughout the study population for 1968-71 is confirmed for 1972-74 as is the excess for lung cancers. The greater excess in the tyre sector is also confirmed, particularly in those men in the 55-64 year age group and those who entered the industry between 1950 and 1960. While men employed in 1967 on moulding, press, autoclave, and pan curing, and workers in finished goods, stores, packaging, and despatch continue to have more lung cancer deaths than expected for 1972-74, the excess is no longer statistically significant. An excess of cancer of the stomach which was overlooked in 1968-71 is not confirmed in 1972-74 but is nevertheless high when the total period of study 1968-74 is considered. The limitations of the study are discussed with particular reference to extrapolating the results to the whole industry. We conclude that there is a higher rate of lung cancer in the tyre sector of the industry and that immediate investigations are required to test the hypothesis concerning the recent excess of bladder cancers. Attention should now be paid to the control of exposures to all potential hazards in the industry.
PMCID: PMC1008147  PMID: 999799
3.  Mortality experience of workers exposed to vinyl chloride monomer in the manufacture of polyvinyl chloride in Great Britain. 
Identification particulars were obtained for over 7000 men who were at some time between 1940 and 1974 exposed to vinyl chloride monomer in the manufacture of polyvinyl chloride. Approximately 99% of these men have been traced and their mortality experience studied. The overall standardised mortality ratio, 75-4, shows a significant reduction compared with the national rates. Four cases of liver cancer were found. Two of these have been confirmed by a panel of liver pathologists as angiosarcoma and two as not angiosarcoma. There is no evidence to support the hypothesis that cancers other than those of the liver are associated with exposure to vinyl chloride monomer. The two cases of angiosarcoma were found in men who had been exposed to high concentrations of the monomer although the second man died only eight years after first exposure. The industry in Great Britain has expanded considerably since the second world war with over 50% of men having entered with the last decade. Conclusions drawn about the effect of vinyl chloride monomer on the mortality experience of men in this industry must consequently be tempered by the reservation that the full impact may not yet be in evidence.
PMCID: PMC1008165  PMID: 557328

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