Biomedical subjects

Geoffrey Berry

Publications and source records attributed to Geoffrey Berry.

9 recordsLinked to original sources

PubMed2007

Relative risk and acceleration in lung cancer.

For a substance that increases the relative risk of disease, it does not necessarily follow that the proportion of cases due to exposure to the substance is the same as the attributable fraction in the exposed. An alternative explanation is that the substance has accelerated the occurrence of disease and, therefore, played a role in all cases. When the incidence of disease with time follows the Weibull distribution, it is well known that the proportional hazards model and the accelerated failure time model are equivalent. The purpose of this paper is to provide a numerical illustration of the relationship between the relative risk and the acceleration time of occurrence of cases. A Weibull distribution is a good approximation for lung cancer death rates up to the age of 80 years. The numerical relationship between the relative risk and the time by which cases are accelerated is given for lung cancer deaths occurring at ages of 40-75 years with relative risks of 1.01-3. As an example, for a death due to lung cancer at age 60 years in a smoker, relative risks of 2 and 1.1 due to occupational exposure to a substance correspond to accelerations of 5.2 years and 8 months, respectively.

Adult↗

PubMed2006

Comparing the part with the whole: should overlap be ignored in public health measures?

BACKGROUND: In public health, health outcomes such as cancer incidence or mortality of subgroups are often compared with health outcomes of the whole population. Our objective was to explore the effect of overlap that occurs in such comparisons and to develop a correction factor to adjust the test statistics and confidence intervals to allow for the effect in situations where the full data are not available. METHOD: The standard error of a difference between a statistic calculated for a subgroup and for the whole population was derived theoretically both ignoring and allowing for overlap. The ratio of these standard errors was defined as the correction factor. Cancer incidence and death data (1997-2001) for the Australian state of New South Wales (NSW) were examined to demonstrate the utility of the correction factor. RESULTS: If the overlap is ignored, significance tests are conservative and confidence intervals too wide. In an example with an overlap of 12%, the correction factor was 1.13 and the significance level of 0.08 was corrected to 0.05 by taking the overlap into account. CONCLUSIONS: The overlap may not be of concern if the result is significant or if the subgroup is <10% of the whole population, but if the overlap is greater than 10% it should not be ignored. The easiest way of allowing for overlap is to use a correction factor, calculated from the amount of overlap, to adjust analyses that ignore overlap.

Confidence Intervals↗

PubMed2005

Nonuniform risk of bloodstream infection with increasing central venous catheter-days.

OBJECTIVE: To determine whether the conventional rate for central venous catheter (CVC)-associated bloodstream infection (BSI) accurately reflects risk for patients exposed for a variety of in situ periods. PATIENTS AND METHODS: Intensive care unit patients (n = 1,375) were monitored for 7,467 CVC-days. They were monitored until catheter removal, until diagnosis of CVC-associated BSI, or for 24 hours after discharge. RESULTS: The BSI rate was 3.7 per 1,000 CVC-days. Ninety-three percent of these patients had CVCs in situ for 1-15 days. These patients were exposed to 59.7% of all CVC-days; the remaining 7% were exposed to 40.3% of all CVC-days. BSI rates stratified by exposure periods of 1-5 and 6-15 days were 2.1 and 4.5 per 1,000 CVC-days, respectively. The rates for 16-30 and 31-320 days were 10.2 and 2.1 per 1,000 CVC-days, respectively. The probability of BSI with a CVC in situ was 6 in 100 by day 15, 14 in 100 by day 25, 21 in 100 by day 30, and 53 in 100 by day 320. CONCLUSION: The conventional aggregated rate better reflects the risk for the majority of patients rather than for patients exposed to the majority of CVC-days. It does not reflect the true probability of risk for all exposures, especially beyond 30 days. CVCs in situ from 1 to 15 days had less risk of BSI than CVCs in situ more than 15 days, which may explain why scheduled CVC replacement at days 5 to 7 has not been found beneficial.

Catheterization, Central Venous↗

PubMed2004

A randomized controlled trial of cyclosporine withdrawal in renal-transplant recipients: 15-year results.

BACKGROUND: In renal transplantation, the immunosuppressive efficacy of cyclosporine is counterbalanced by its nephrotoxicity. Although cyclosporine improves short-term graft survival, its long-term effects are unclear. METHODS: Recipients of first cadaver renal transplants were randomized into three groups between 1983 and 1986: azathioprine and prednisolone alone (AP, n = 158), long term cyclosporine alone (Cy, n = 166), and short-term cyclosporine followed by azathioprine and prednisolone (CyAP, n = 165). All groups received methylprednisolone induction. RESULTS: There were no significant differences in patient survival at 15 years (48 vs. 56 vs. 51%, P = 0.14), and 15-year graft survival (censored for death) in those patients in the CyAP group (47 vs. 44 vs. 59%, P = 0.06) was not significantly different statistically. When deaths or graft losses before 12 months were censored, the differences in 15-year graft survival between the groups were significant (58%, 51%, 70%, P = 0.01). The CyAP group also had lower mean serum creatinine at all time points beyond 3 months posttransplant out to 10 years (143 vs. 169 vs. 131 micromoles/L, P = 0.04). Per protocol analysis, after censoring patients at change in therapy, increased the observed differences in 15-year graft survival between the groups (54 vs. 38 vs. 65%, P = 0.01). CONCLUSION: Survival and function of first cadaveric kidney transplants is improved by use of short-term cyclosporine followed by azathioprine and prednisolone. Long-term cyclosporine use reduces long-term graft survival.

Adult↗

PubMed2004

Silicosis and lung cancer: a mortality study of compensated men with silicosis in New South Wales, Australia.

BACKGROUND: Lung cancer mortality has been found to be in excess in several groups with silicosis, but allowance for smoking was not always possible. We investigated the lung cancer mortality in men with silicosis in New South Wales, Australia, who were compensated, making allowance for smoking habits. METHODS: A mortality study of 1467 men with silicosis in New South Wales who were compensated was carried out comparing observed mortality with that expected from the New South Wales death rates adjusting for age and period. Their smoking habits were compared with national survey smoking rates and the expected number of lung cancer deaths adjusted for smoking. Cases were coded for occupation and industry. RESULTS: The observed mortality was higher than expected, but the only site of cancer showing a significant excess was the lung. The group with silicosis had smoked more than the national rates. After adjusting for smoking the standardized mortality ratio for lung cancer was 1.9 (95% confidence interval 1.5-2.3). Although there were differences in lung cancer mortality between industries and occupations, these differences were not statistically significant. CONCLUSIONS: The excess lung cancer death rate may not be entirely due to silica exposure because compensation may have been influenced by the presence of chronic obstructive respiratory disease and there is some evidence that the presence of this disease increases lung cancer risk independently of smoking.

Aged↗

PubMed2003

Health impacts of pesticide exposure in a cohort of outdoor workers.

We compared mortality of 1,999 outdoor staff working as part of an insecticide application program during 1935-1996 with that of 1,984 outdoor workers not occupationally exposed to insecticides, and with the Australian population. Surviving subjects also completed a morbidity questionnaire. Mortality was significantly higher in both exposed and control subjects compared with the Australian population. The major cause was mortality from smoking-related diseases. Mortality was also significantly increased in exposed subjects for a number of conditions that do not appear to be the result of smoking patterns. Compared with the general Australian population, mortality over the total study period was increased for asthma [standardized mortality ratio (SMR) = 3.45; 95% confidence interval (CI), 1.39-7.10] and for diabetes (SMR = 3.57; 95% CI, 1.16-8.32 for subjects working < 5 years). Mortality from pancreatic cancer was more frequent in subjects exposed to 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (SMR = 5.27; 95% CI, 1.09-15.40 for subjects working < 3 years). Compared with the control population, mortality from leukemia was increased in subjects working with more modern chemicals (standardized incidence ratio = 20.90; 95% CI, 1.54-284.41 for myeloid leukemia in the highest exposure group). There was also an increase in self-reported chronic illness and asthma, and lower neuropsychologic functioning scores among surviving exposed subjects when compared with controls. Diabetes was reported more commonly by subjects reporting occupational use of herbicides. These findings lend weight to other studies suggesting an association between adverse health effects and exposure to pesticides.

Adult↗

PubMed2002

Analytic methods for comparing two dichotomous screening or diagnostic tests applied to two populations of differing disease prevalence when individuals negative on both tests are unverified.

Two dichotomous screening tests may be compared by applying both tests to all members of a sampled population. For individuals with a positive result on either test the disease status may be verified by a reference standard, but for individuals negative on both tests the disease status may be unverified because the probability of disease is so low that further investigation is costly, unacceptable and perhaps unethical. If the tests have been applied to samples from two populations which have different disease prevalences then unbiased estimates of the true positive and false positive rates of each test, the prevalences in the two populations, and two parameters representing dependence between the two tests can be estimated using maximum likelihood methods. The methods are based on the assumption that the sensitivities and specificities of the two tests, and the dependencies between the tests, are independent of prevalence. A test of goodness of fit provides a test of this.

Adult↗

PubMed2002

Socio-economic mortality differentials in Sydney over a quarter of a century, 1970-94.

OBJECTIVE: To examine trends in socio-economic differentials in all-cause mortality in Sydney over a 25-year period (1970-94). METHODS: Five measures of single indicators (two for occupation, two for education and one for income) and a composite measure of socio-economic disadvantage based on Census data (the Australian Bureau of Statistics' Index of Relative Socio-Economic Disadvantage) were used as indicators of socio-economic status by local govemment area. The relationship between mortality and socio-economic status was examined using quintiles based on these six measures of socio-economic status. RESULTS: Socio-economic differentials in mortality were evident for males and females for all periods, and over the 25-year period the relative socio-economic differentials did not decline. For males, the socio-economic status differential in mortality widened, irrespective of socio-economic status indicator used, whereas for females it widened only when certain socio-economic indicators were used: occupation (unemployment measure) and income, but was not significant for the other single indicators or for the composite indicator. CONCLUSIONS: Sydney trends of widening inequalities are generally similar to those reported for Britain and for other industrialised countries, suggesting that this is a common phenomenon and that policies to reduce health inequalities over the past quarter of a century have not been effective.

Adolescent↗

PubMed2002

Differences in muscle fiber growth in slow-twitch muscles of the forelimb and hindlimb of the rat: role of the pituitary and food intake.

This investigation tested the hypothesis that differences in the growth of fore- and hindlimb muscles in the rat are regulated by the pituitary and food intake. Using morphometric techniques, the growth of muscle fibers was compared in two slow-twitch muscles, the flexor carpi ulnaris (FCU) of the forelimb, and the soleus of the hindlimb, in male Wistar rats fed ad libitum, food restricted (FR) or hypophysectomized (hypox) from age 60 days. Growth was defined as an increase in fiber diameter and/or type 1 fiber percentage. The soleus had larger diameter fibers than the FCU in controls and FR, but not hypox rats. The growth in diameter, between 60 and 180 days, of both types 1 and 2 fibers in the soleus and type 2 fibers in the FCU was inhibited by hypox and, to a lesser extent, FR. Neither type 1 fiber diameter nor percentage of type 1 fibers in the FCU increased with age nor was it affected by hypox or FR. The percentage of type 1 fibers was higher in the soleus than the FCU and was further increased in the soleus of hypox rats. Food restriction produced a smaller rise than hypox in type 1 fiber percentage in the soleus. Thus, differences in fore- and hindlimb muscle fiber growth are modulated by pituitary hormones and, to a lesser extent, by food intake.

Animals↗