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Colin R Muirhead

Publications and source records attributed to Colin R Muirhead.

8 recordsLinked to original sources
PubMed2006

Possible selection effects for radiation risk estimates in Japanese A-bomb survivors: reanalysis of acute radiation symptoms data.

An earlier analysis examined the possibility of bias in the Life Span Study (LSS) cohort by studying Japanese A-bomb survivors with bomb-related acute injuries and those without such injuries. The authors reported significantly higher radiation risks, both for cancers and non-cancers, among those survivors with acute injuries compared with those without. The risks were reported to be particularly large among survivors aged <10 or > or =55 years of age at the time of bombings. The aim of this paper is to examine these findings more closely using the LSS acute effects data. All the analyses were carried out using Poisson regression. Relative risk models were fitted with adjustment for sex and other factors. Significant differences in relative risk between survivors with epilation and burns and those without epilation and burns are found for leukaemia. There is also some evidence for heterogeneity in the leukaemia risk between survivors with two or more acute injuries and those with no injuries, but the evidence is disappeared when survivors with one or more injuries are compared with those without injuries. For solid cancers, cardiovascular disease and all deaths combined, the risks do not differ to a statistically significant extent between survivors with and without injuries. There is no statistically significant heterogeneity in risk across age-at-exposure categories for survivors with injuries. For all deaths combined, relative risk estimates and their uncertainties are significantly higher for survivors exposed at ages <10 years when compared with other exposure ages, but risks are not significantly raised for survivors exposed at > or =55 years of age. With the exception of leukaemia, the findings from the present work are inconsistent with those of Stewart and Kneale.

Adult↗
PubMed2006

Methods for detecting disease clustering, with consideration of childhood leukaemia.

In trying to interpret reports of disease clusters in specific localities, it is valuable to know whether the disease in question has a general tendency to cluster spatially. Methods for investigating localized disease clustering were the subject of a comparative study organized by the International Agency for Research on Cancer some years ago. This paper addresses some further aspects of one of the methods used in this exercise, namely the Potthoff-Whittinghill (P-W) test. Particular consideration is given to methodology for estimating the magnitude of overdispersion and for detecting whether one area, in particular, has an undue influence on the evidence for overdispersion using the P-W test, the extent to which is possible to detect clustering over regions of differing sizes using a components-of-variance approach and how adjustment for overdispersion might affect tests for raised disease rates in specific locations. These points are illustrated using data on childhood leukaemia incidence and reference is made to other analyses of the geographical distribution of childhood leukaemia that are based on this approach.

Adolescent↗
PubMed2005

Age-at-exposure effects on risk estimates for non-cancer mortality in the Japanese atomic bomb survivors.

Statistically significant increases in non-cancer disease mortality with radiation dose have been observed among survivors of the atomic bombings of Hiroshima and Nagasaki. The increasing trends arise particularly for diseases of the circulatory, digestive, and respiratory systems. Rates for survivors exposed to a dose of 1 Sv are elevated by about 10%, a smaller relative increase than that for cancer. The aetiology of this increased risk is not yet understood. Neither animal nor human studies have found clear evidence for excess non-cancer mortality at the lower range of doses received by A-bomb survivors. In this paper, we examine the age and time patterns of excess risks in the A-bomb survivors. The results suggest that the excess relative risk of non-cancer disease mortality might be highest for exposure at ages 30-49 years, and that those exposed at ages 0-29 years might have a very low excess relative risk compared with those exposed at older ages. The differences in excess relative risk for different age-at-exposure groups imply that the dose response relationships for non-cancer disease mortality need to be modelled with adjustment for age-at-exposure.

Adolescent↗
PubMed2003

Fitting the two-stage model of carcinogenesis to nested case-control data on the Colorado Plateau uranium miners: dependence on data assumptions.

This paper investigates some problems with the Colorado Plateau uranium miners cohort when fitting the mechanistic model of carcinogenesis of Moolgavkar et al. (MVK model) to nested case-control data for lung cancers. The influence of data for hard rock mining and work histories on the model fitting is examined and found to be highly influential. The question of selecting the most appropriate number of controls per case is also considered. Analyses were carried out assuming that the hard rock mining exposure occurred prior to all other work histories and that miners received no exposure between work histories. The use of less than 15 controls per case was found to seriously restrict the quality of fit of the models. The best fitting, most reliable model contained linear effects of radon exposure on the first mutation rate, the rate of differentiation, and the rate of death of the intermediate cells. An effect of smoking on the growth of the intermediate cells was also included in the model. It is concluded that owing to the complexity of the MVK model and the limited amount of information in this dataset, the reliability of the Colorado Plateau dataset for fitting this type of model, particularly in a case-control format, is questionable.

Case-Control Studies↗