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Biomedical subjects

S W Duffy

Publications and source records attributed to S W Duffy.

At least 19 recordsLinked to original sources
PubMed1992

Pickled vegetables in the aetiology of oesophageal cancer in Hong Kong Chinese.

Oesophageal cancer is common in Chinese populations, but individual-based epidemiological studies have provided little explanation. A case control study with 400 cases and 1598 controls (800 hospital and 798 general practice) was conducted among Hong Kong Chinese. In multivariate analyses, statistically significant effects on risk were detected for several potentially preventable exposures with high attributable risks (ARs). These included preference for consuming drinks or soups at high temperature (AR = 14%), infrequent consumption of green leafy vegetables (AR = 15%) and citrus fruits (AR = 26%), ingestion of pickled vegetables (AR = 29%), tobacco smoking (AR = 44%), and alcohol drinking (AR = 48%). On the assumption of multiplicative risk, the combined AR due to these exposures was 89%. This is the first case control study to show an association between pickled vegetable consumption and oesophageal cancer risk. The finding considerably strengthens the evidence for carcinogenicity of N-nitroso compounds in man and helps to explain the very high risk among Chinese.

Aged↗
PubMed1992

Cluster randomization in large public health trials: the importance of antecedent data.

Large-scale public health trials are often randomized by geographic or administrative clusters, for reasons of financial or organizational exigency. In this paper, we deal with the situation where the dependent variable is a count of events, such as mortality from, or incidence of a given disease. Simulation results show that this design may decrease power by more than 50 per cent. The lost power can largely be replaced by incorporating information on the dependent variable, within clusters, before the start of the trial. The pretrial and trial data can be analysed by negative trinomial models.

Breast Neoplasms↗
PubMed1992

Risk factors for breast cancer by age and menopausal status: a case-control study in Singapore.

A case-control study was conducted among Singapore Chinese women, comprised of 200 histologically confirmed cases of breast cancer and 420 hospital controls. Subjects were interviewed on family history of breast cancer, social and demographic characteristics, reproductive history, and diet one year prior to interview. Differences in risk factors were observed according to menopausal status. In the premenopausal group, the most consistently significant nondietary effect was an increased risk with late age at first birth. In postmenopausal women, the most consistent nondietary effects were increased risks with nulliparity, tall stature, high educational status, and a family history of breast cancer. In premenopausal women, the strongest dietary effects were low risks with high intakes of polyunsaturated fatty acids (PUFA), beta-carotene, soya protein as a proportion of all protein, and a high risk with high red-meat intake. No dietary effects were observed in postmenopausal women. Examination of effects by 10-year age groups suggested that the differences in the effects of age at first birth, nulliparity, height, education, beta-carotene intake, and PUFA intake between premenopausal and postmenopausal women were at least partly attributable to age-related differences in the baseline distributions of these variables. The variation in the effects of red meat and soya protein appeared to be attributable mainly to menopausal status itself, which is consistent with the hypothesis that these factors operate on risk by way of hormonal mechanisms.

Adult↗
PubMed1992

Combined inter-observer and inter-method variation in bone histomorphometry.

Manual methods for the measurement of bone biopsies have largely been superseded by semi-automatic computerised techniques. Histomorphometrists often use control data obtained by other observers using different methods, thus combining inter-observer and inter-method variation. We have examined the combined effect of inter-method and inter-observer variation on measurements of bone area, osteoid perimeter, and osteoid width in iliac crest biopsies from healthy subjects, one observer using the manual grid system and the other using a semi-automated technique. Inter-observer and inter-method variation were independently determined, and the proportion of each expressed as a percentage of combined error. Our results indicate that the combination of inter-method and inter-observer variation causes significant differences in the values obtained for osteoid perimeter, whereas inter-method variation is mainly responsible for differences in osteoid width values; differences in bone area are largely due to inherent sampling variation. These variations indicate that caution is required when comparison is made with control data from other sources, especially if different techniques are employed.

Analysis of Variance↗
PubMed1992

Oesophageal cancer in the Republic of Karakalpakstan.

Regional and temporal patterns of variation in the incidence of cancer of the oesophagus in the Central Asian republic of Karakalpakstan were analysed. Karakalpakstan (population about 1200,000) is an area with high rates of this disease. Incidence data within regions (data from 1988-1989), ethnic groups (data from 1987-1989) and calendar periods (data from 1973-1987) were available for analysis, with corresponding official population estimates. No significant difference was observed between rates in urban and rural environments, although significant regional variation was observed (P less than 0.05). The highest rate observed was in the Muinak, the northern region, with world age-standardized rates (ASR) of 125.96 for males and 150.65 for females. There was a very significant difference among ethnic groups (P less than 0.001). The ethnic group with the highest incidence was the Kazakh people, with an ASR of 68.0 in males and 86.3 in females. Incidence in the republic as a whole declined in the period from 1973 to 1987. Incidence of cancer of the oesophagus is still high in Karakalpakstan, despite the decline. Incidence is likely to be strongly related to factors associated with region of residence and with ethnicity.

Adolescent↗
PubMed1992

External validation, repeat determination, and precision of risk estimation in misclassified exposure data in epidemiology.

STUDY OBJECTIVE: The aim was to quantify the difference in precision of risk estimates in epidemiology between the situations where misclassification of exposure is corrected for by external validation and where it is corrected for by internal repeat measurement. Precision was measured in terms of the expected width of the 95% confidence interval on the odds ratio. DESIGN: In a hypothetical case-control study, first with 100 cases and 100 controls, then with 100 cases and 1000 controls (the latter to approximate the cohort study situation), expected estimated odds ratios and confidence intervals were calculated based on postulated underlying true odds ratios and misclassification error rates. The sizes of the confidence intervals using the two design strategies were compared, based on the same number of subjects receiving internal repeat measurements as were used in the external validation study. MAIN RESULTS: Confidence intervals obtained using internal repeat measurement were considerably narrower than those using external validation. Both methods yielded approximately correct point estimates. CONCLUSIONS: In terms of precision, it is preferable to correct for misclassification using internal repeat measurement rather than external validation.

Analysis of Variance↗
PubMed1992

Update of the Swedish two-county program of mammographic screening for breast cancer.

The results of the Swedish two-county trial of mammographic screening for breast cancer are presented, updated to December 31, 1990, which is an average of 10.8 years follow-up per person. The main result of the trial in terms of breast cancer mortality remained the same: compared with the control group, the group invited to screening had a relative breast cancer mortality of 0.70 (P = 0.0002) with 95% confidence interval (0.58, 0.85). Analysis of survival showed that relative to the control group, the cancers detected at prevalence screen, incidence screens, and in the interval between screens had a good prognosis, whereas cancers detected in those who had refused screening had a very poor prognosis. When adjusted for tumor size, lymph node status, and tumor grade (differentiation), the better survival associated with incidence screen and interval detection was largely accounted for, indicating that the benefit of incidence screening is largely achieved through the effect of screening on the three prognostic variables, notably size of the tumor. Results indicate that to achieve a substantial mortality reduction, 50% of screen-detected invasive cancers should be less than 15 mm in diameter, at least 30% of screen-detected grade 3 tumors should be less than 15 mm, and at least 70% of screen-detected tumors should not have lymph node metastases. The percentage of grade 3 tumors of a given size should be the same in screen-detected cancers as in clinically detected, and breast cancer prevalence at first screen should be at least three times the expected incidence rate in the absence of screening. This should be achieved without the recall rate for further examination exceeding 9%, and procedures including further imaging techniques and fine needle aspiration or core biopsy should be used before resorting to surgical biopsy. These aims can be achieved in specialist screening centers if particular attention is paid to resources for screening and diagnostic evaluation, specialist training of clinical and technologic screening staff, and ongoing monitoring of mammographic quality, recall rates, and the attributes of the tumors detected.

Adult↗
PubMed1991

Risk factors for cancer of the oesophagus in Kerala, India.

A case-control study of oesophageal cancer was carried out in Trivandrum, Kerala, involving 267 cases and 895 controls. Risk factors studied in males were pan (betel)-tobacco chewing, bidi and cigarette smoking, drinking alcohol and taking snuff. Only pan-tobacco chewing was investigated in females as very few indulged in the other habits. Among males significant associations with higher risk were observed for bidi smoking (p less than 0.001), bidi plus cigarette smoking (p greater than 0.05) and drinking alcohol (p less than 0.001). While a significant effect of duration of pan-tobacco chewing (p less than 0.005) was observed in males, there was no significant trend, the risk first falling then rising as duration of use increased. This was partly due to confounding with smoking. No effect of pan-tobacco use was observed in females. A step-wise model was fitted, retaining only those risk factors which were significant when adjusted for other factors; the risk factors included were duration of pan-tobacco chewing, duration of bidi smoking, daily frequency of bidi and cigarette smoking and alcohol use (yes or no). An adjusted relative risk of 2.03 was observed for a pan-tobacco habit of more than 40 years' duration, of 4.70 for more than 20 years of bidi smoking, of 4.80 for more than 20 bidis/cigarettes per day, and of 2.33 for regular alcohol use (in each category relative to a baseline of those never indulging in the relevant habit).

Adult↗
PubMed1991

Diet, alcohol consumption and reproductive factors in a case-control study of breast cancer in Moscow.

A case-control study was conducted in Moscow to assess the effect of diet on risk of breast cancer, and also to study the established reproductive risk factors. A notable finding of the study, which covered 139 case-control pairs matched by age and neighbourhood, is that dietary factors are more important for post-menopausal than for pre-menopausal breast cancer. The decreased risk of post-menopausal breast cancer was associated with high intakes of cellulose (OR 0.04; 95% CI 0.01-0.31), mono- and disaccharides (OR 0.02; 95% CI 0.002-0.27), vitamin C (OR 0.20; 95% CI 0.06-0.70), beta-carotene (OR 0.09; 95% CI 0.02-0.49), and also polyunsaturated fatty acids (OR 0.14; 95% CI 0.03-0.69). High intakes of total fat resulted in a statistically non-significant decrease in the odds ratio (OR 0.52; 95% CI 0.04-6.99), while saturated fats slightly increased the risk of breast cancer (OR 1.67; 95% CI 0.24-11.78). Protein intake was also associated with increased risk of breast cancer (OR 4.62; 95% CI 0.69-30.70). Alcohol use significantly increased the risk of breast cancer in postmenopausal women (OR 3.39; 95% CI 1.37-8.38). In general, the results of our study indicate that high risk of breast cancer is associated with high intakes of nutrients derived from animal products, and low risk with high intake of those from vegetables and fruits.

Adult↗
PubMed1991

Dietary effects on breast-cancer risk in Singapore.

It is suspected that diet influences the risk of getting breast cancer. A study of diet and breast cancer was done among 200 Singapore Chinese women with histologically confirmed disease and 420 matched controls. A quantitative food-frequency questionnaire was used to assess intakes of selected nutrients and foods 1 year before interview. Daily intakes were computed and risk analysed after adjustment for concomitant risk factors. In premenopausal women, high intakes of animal proteins and red meat were associated with increased risk. Decreased risk was associated with high intakes of polyunsaturated fatty acids (PUFA), beta-carotene, soya proteins, total soya products, a high PUFA to saturated fatty acid ratio, and a high proportion of soya to total protein. In multiple analysis, the variables which were significant after adjustment for each other were red meat (p less than 0.001) as a predisposing factor, and PUFA (p = 0.02), beta-carotene (p = 0.003), and soya protein (p = 0.02) as protective factors. The analysis of dietary variables in postmenopausal women gave uniformly non-significant results. Our finding that soya products may protect against breast cancer in younger women is of interest since these foods are rich in phyto-oestrogens.

Adult↗
PubMed1991

Repeat measurement of case-control data: correcting risk estimates for misclassification due to regression dilution of lipids in transient ischemic attacks and minor ischemic strokes.

In a case-control study to determine the role of lipids as risk factors for ischemic cerebrovascular disease, 105 cases of transient ischemic attacks and minor ischemic strokes were compared with 241 controls. Recruitment to the study took place in Oxford, United Kingdom, in 1986 and 1987. In a random subset of 100 of the original controls, repeat assays of total cholesterol, low density lipoprotein cholesterol, (LDL cholesterol), and high density lipoprotein cholesterol (HDL cholesterol) were performed. With maximum likelihood theory, the repeat data were used to produce odds ratio estimates of relative risk corrected for mismeasurement. Uncorrected odds ratios associated with total cholesterol of more than 6 mmol/liter, LDL cholesterol of more than 3.5 mmol/liter, and HDL cholesterol of more than 1.2 mmol/liter were, respectively, 2.06 (95% confidence interval (CI) 1.26-3.37), 2.02 (95% CI 1.24-3.30), and 0.46 (95% CI 0.28-0.74). Corrected for mismeasurement, the corresponding odds ratios were 2.90 (95% CI 1.42-5.93), 2.57 (95% CI 1.24-5.32), and 0.36 (95% CI 0.17-0.71), respectively. The attributable risks changed from 34 to 48% for total cholesterol, from 34 to 43% for LDL cholesterol, and from 35 to 45% for HDL cholesterol. The maximum likelihood procedure described here corrects for substantial underestimation of the strength of an association and indicates the need to obtain repeat measurements on variables which are subject to random fluctuation.

Case-Control Studies↗
PubMed1991

Breast screening, prognostic factors and survival--results from the Swedish two county study.

The results of the Swedish two-county study are analysed with respect to tumour size, nodal status and malignancy grade, and the relationship of these prognostic factors to screening and to survival. It is shown that these factors can account for much of the differences in survival between incidence screen detected, interval and control group cancers but to a lesser extent for cancers detected at the prevalence screen where length bias is greatest. Furthermore, examination of the relationships among the prognostic factors and mode of detection indicates that malignancy grade, as a measure of inherent malignant capacity, evolves as a tumour grows. The proportion of cancers with poor malignancy grade is several fold lower for cancers of diameter less than 15 cm than for cancers greater than 30 cm, independent of the length bias of screening. The implications of these findings for screening frequency are briefly discussed.

Adult↗
PubMed1991

Modelling the analysis of breast cancer screening programmes: sensitivity, lead time and predictive value in the Florence District Programme (1975-1986).

Statistical indicators of early efficacy were estimated in the Florence District Programme where breast cancer screening has been carried out since 1970. Analysis of screen-detected and interval cancer data by means of statistical modelling using GLIM allowed us to estimate the mean sojourn time (1.91 and 3.97 years in 40-49 and 50-69 year old women respectively), sensitivity (about 90% for those aged 50-69) and predictive value at the prevalence screening test (about 100%). Results were compared with estimates of the same parameters in the Health Insurance Plan and Swedish Two County studies.

Adult↗