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M Blettner

Publications and source records attributed to M Blettner.

At least 73 records · Page 4Linked to original sources
PubMed1995

Occupation, smoking and demographic factors, and renal cell carcinoma in Germany.

BACKGROUND: The role of occupational exposure in the aetiology of renal cell cancer is still not clear. In a population-based, case-control study we investigated occupational and smoking history as well as place of residence, marital and socioeconomic status. METHOD: In a case-control study in Germany, 277 adult cases with incident renal cell cancer and 286 controls frequency-matched to the cases for age and gender have been interviewed. The data were analysed by standard methods using unconditional logistic regression models, to estimate the relative risk (RR) and the corresponding 95% confidence interval (95% CI). RESULTS: Socioeconomic status was inversely associated (RR = 0.61, 95% CI: 0.3-1.2 for highest category) with the risk for renal cell cancer. Heavy smoking gave an increased, but not significant (about twofold) RR in men and women for ex-smokers and current smokers. Employment in metal-related industries (RR = 1.63, 95% CI: 1.1-2.5) was also identified as a risk factor. Additionally, we found an elevated risk associated with exposure to perchloroethylene and tetrachlorocarbonate (RR = 2.52, 95% CI: 1.2-5.2) but no time trend could be observed. No associations were found for other occupational exposures, such as working in the chemical industry, transportation or farming nor for exposure to pesticides. CONCLUSIONS: The results of our study lead to the suggestion that smoking, occupation and demographic factors probably play a minor role in the aetiology of renal cell cancer.

Adult↗
PubMed1994

[Trend analysis in Hodgkin disease mortality in the German Federal Republic 1955-1989: a comparison of log-linear models with descriptive standard methods].

Age-Period-Cohort (APC) models have become a widely accepted method to analyse incidence and mortality rates of cancer or other diseases. In this paper we compare simple descriptive methods such as plotting age-specific rates and standardized rates with regression models in order to investigate mortality rates of Morbus Hodgkin's disease in Germany (West-Germany) between 1955 and 1989. With any of the approaches it can be seen that the mortality of Morbus Hodgkin's disease has been decreasing around 1970. Although APC-models allow some detailed investigation of the separate influence of the age, period and cohort effect, the results are difficult to interpret as there is no unique solution for the parameter estimates (identification problem of APC-models). For the mortality of Morbus Hodgkin's, the result of the APC-modelling shows that the decrease of mortality is overestimated if the cohort effect is not taken into consideration. We therefore conclude that the interpretation of the APC-model should be done in connection with other methods to avoid misinterpretation. The combination of both approaches will lead to a better understanding of the incidence or mortality patterns of cancer.

Adult↗
PubMed1993

Misclassification bias arising from random error in exposure measurement: implications for dual measurement strategies.

Despite the resulting loss of information, continuous exposure variables are often categorized in epidemiologic data analysis. It has been shown that nondifferential measurement error of exposure can lead to differential misclassification under these circumstances. This paper extends these findings to the misclassification bias that results from nondifferential measurement error if dual measurement strategies are employed with dichotomized exposures. Different scenarios of random measurement error are presented in the context of case-control studies. Although differences in the misclassification rates between cases and controls are generally small, the bias toward the null is usually much weaker than expected under truly nondifferential exposure misclassification even with single exposure measurements. In most cases, the bias is further reduced by the use of dual measurements. Caution is needed, however, if the analysis is restricted to individuals with concordant exposure classifications (both measurements above or both measurements below the cutpoint). In this case, the true exposure-disease association is often overestimated.

Bias↗
PubMed1993

Influence of model-building strategies on the results of a case-control study.

We evaluate the analysis of a case-control study in which many variables were investigated simultaneously. The purpose of the study was to explore some rather unspecific hypotheses about potential risk factors for adult brain tumour. Our aim is to show that in the analysis of case-control studies many decisions are necessary which are usually not published in detail. As in most studies these decisions are made during analysis and are data dependent. We demonstrate that the data allow sensible alternative decisions which influence the final results. A sensitivity analysis of several aspects of the analysis such as different measurement scales, variable selection, handling of missing values and interactions was performed, and demonstrated variation in the results based on the strategy for analysis. We conclude that details of the final analysis should be decided in the planning phase of a case-control study, and that more details of model-building strategies must be published. Results from a study where the analysis is highly data dependent must be interpreted with caution and validation of the results with new studies is essential.

Bias↗
PubMed1993

Dietary carcinogens and the risk for glioma and meningioma in Germany.

A population-based case-control study was performed in South-West Germany in 1987/88 with 115 histological confirmed glioma and 81 meningioma cases and 418 randomly selected controls. On the basis of information from a food-frequency questionnaire and questions on food preparation and food supply, the role of dietary carcinogens, in particular N-nitroso compounds or their precursors, on risk for glioma and meningioma were analyzed by multiple logistic regression. Eleven food groups were investigated. The intake of processed meat was significantly associated with an increased risk of glioma. The intake of any food group was not significantly related to meningioma risk. Among single meat products, a significantly higher risk of glioma was found for cooked ham, processed pork meat and fried bacon. For the consumption of 3 N-nitrosamines, assessed from the intake of processed meat and cheese, significant positive relations to glioma risk were found. These N-nitrosamines were also related to meningioma risk, although to a less pronounced extent. The risk for occurrence of glioma was significantly increased for those using vegetable fat frequently for deep frying, as compared with non-users. For the dietary intake of nitrate, nitrite, vitamin C, specific alcoholic beverages, total alcohol, and water from a non-central supply, no elevated risk was found in this study.

Alcohol Drinking↗
PubMed1992

Association between brain tumors and menopausal status.

BACKGROUND: Several lines of evidence have implicated female hormones in the etiology of human brain tumors, meningiomas in particular. PURPOSE: To investigate the relationship between brain tumor development and the hormonal changes manifested during pregnancy and menopause, we analyzed data from female participants in a population-based case-control study of adult brain tumors. This study was conducted in 1987-1988 in the Rhein-Neckar-Odenwald area of the Federal Republic of Germany. METHODS: The study population consisted of 127 women with meningiomas, gliomas, and acoustic neuromas (case patients) and 233 control women who were selected from the general population and frequency-matched by age to the case patients. Information on parity, menopausal status, and previous gynecologic surgeries was obtained through a standardized questionnaire. Case patients and control subjects were compared with the use of the unconditional maximum likelihood estimation of the parameters in a logistic regression model. RESULTS: Our results were not statistically significant; nevertheless, they revealed some interesting trends. No association was found between parity and the development of any of the three histological subtypes of brain tumor (relative risk [RR] = 1.31; 95% confidence interval [CI] = 0.51-2.07). Menopausal women had a greatly reduced risk of developing meningiomas (RR = 0.58; 95% CI = 0.18-1.90), and this effect was most pronounced when menopause had been surgically induced by bilateral oophorectomy (RR = 0.12; 95% CI = 0.01-1.30). Menopausal women had a greater risk of developing gliomas or acoustic neuromas (RR = 1.77; 95% CI = 0.67-4.68), except when menopause was surgically induced, in which case the risk was reduced (RR = 0.33; 95% CI = 0.04-3.09). Oophorectomy after menopause did not appear to influence risk. CONCLUSIONS: Since the onset of menopause is accompanied by cessation of estrogen production, our results support the notion that female hormones play a role in the development of brain tumors.

Adult↗
PubMed1992

Adjuvant radiotherapy and risk of contralateral breast cancer.

BACKGROUND: The risk of contralateral breast cancer is increased twofold to fivefold for breast cancer patients. A registry-based cohort study in Denmark suggested that radiation treatment of the first breast cancer might increase the risk for contralateral breast cancer among 10-year survivors. PURPOSE: Our goal was to assess the role of radiation in the development of contralateral breast cancer. METHODS: A nested case-control study was conducted in a cohort of 56,540 women in Denmark diagnosed with invasive breast cancer from 1943 through 1978. Case patients were 529 women who developed contralateral breast cancer 8 or more years after first diagnosis. Controls were women with breast cancer who did not develop contralateral breast cancer. One control was matched to each case patient on the basis of age, calendar year of initial breast cancer diagnosis, and survival time. Radiation dose to the contralateral breast was estimated for each patient on the basis of radiation measurements and abstracted treatment information. The anatomical position of each breast cancer was also abstracted from medical records. RESULTS: Radiotherapy had been administered to 82.4% of case patients and controls, and the mean radiation dose to the contralateral breast was estimated to be 2.51 Gy. Radiotherapy did not increase the overall risk of contralateral breast cancer (relative risk = 1.04; 95% confidence interval = 0.74-1.46), and there was no evidence that risk varied with radiation dose, time since exposure, or age at exposure. The second tumors in case patients were evenly distributed in the medial, lateral, and central portions of the breast, a finding that argues against a causal role of radiotherapy in tumorigenesis. CONCLUSIONS: The majority of women in our series were perimenopausal or postmenopausal (53% total versus 38% premenopausal and 9% of unknown status) and received radiotherapy at an age when the breast tissue appears least susceptible to the carcinogenic effects of radiation. Based on a dose of 2.51 Gy and estimates of radiation risk from other studies, a relative risk of only 1.18 would have been expected for a population of women exposed at an average age of 51 years. Thus, our data provide additional evidence that there is little if any risk of radiation-induced breast cancer associated with exposure of breast tissue to low-dose radiation (e.g., from mammographic x rays or adjuvant radiotherapy) in later life.

Adult↗
PubMed1992

Medical risk factors and the development of brain tumors.

Several diseases and medical treatments are discussed as risk factors for the development of brain tumors. A population-based case-control study in the Rhein-Neckar-Odenwald area (containing 1.3 million inhabitants) of Germany was established to investigate this question. A total of 226 patients (cases) with primary brain tumors (International Classification of Diseases, ninth edition, classes 191, 191.1, and 192.0) and 418 control subjects (controls) were interviewed using a standardized questionnaire over a period of 2 years. No association was seen for head injuries, hereditary diseases, family history, and radiographic examination of the head and teeth. However, more cases than controls had had meningitis (relative risk [RR], 2.7; 95% confidence interval [CI], 0.9 to 8.6) or epilepsy (RR, 2.6; 95% CI, 0.6 to 11.7). The RR was decreased for those who had allergic diseases (RR, 0.7; 95% CI, 0.5 to 1.0), diabetes (RR, 0.7; 95% CI, 0.3 to 1.8), and infections and colds (RR, 0.3; 95% CI, 0.1 to 0.8).

Adult↗
PubMed1992

Cancer in the contralateral breast after radiotherapy for breast cancer.

BACKGROUND: Patients with breast cancer have a threefold increase in the risk that a second breast cancer will develop. Radiation treatment for the initial cancer can result in moderately high doses to the contralateral breast, possibly contributing to this heightened risk. METHODS: We conducted a case-control study in a cohort of 41,109 women diagnosed with breast cancer between 1935 and 1982 in Connecticut. We reviewed the medical records of 655 women in whom a second breast cancer developed five or more years after the initial tumor and compared their radiation exposure with that of 1189 matched controls from the cohort who did not have a second cancer. The dose of radiation to the contralateral breast was estimated from the original radiotherapy records. Among the exposed women, the average radiation dose to the contralateral breast was 2.82 Gy (maximum, 7.10). RESULTS: Overall, 23 percent of the women who had a second breast cancer and 20 percent of the controls had received radiotherapy (relative risk of a second breast cancer associated with radiotherapy, 1.19). Among women who survived for at least 10 years, radiation treatment was associated with a small but marginally significant elevation in the risk of a second breast cancer (relative risk, 1.33); the risk increased significantly with the dose of radiation. An increase in risk in association with radiotherapy was evident only among women who were under 45 years of age when they were treated (relative risk, 1.59) and not among older women (relative risk, 1.01). CONCLUSIONS: Radiotherapy for breast cancer contributes little to the already high risk of a second cancer in the opposite breast. Fewer than 3 percent of all second breast cancers in this study could be attributed to previous radiation treatment; the risk, however, was significantly increased among women who underwent irradiation at a relatively young age (less than 45 years). Radiation exposure after the age of 45 entails little, if any, risk of radiation-induced breast cancer.

Adult↗
PubMed1992

Power calculation for cohort studies with improved estimation of expected numbers of deaths.

This paper focuses on improving the accuracy of sample size calculations for cohort studies by careful calculation of the expected number of deaths in the population, taking into account either prior information or realistic assumptions about variables which may affect the mortality or incidence. Sometimes small changes in the assumptions can dramatically alter the expected numbers and may necessitate modifications in the design of the study. Possible modification include extension of the follow-up time, and recognition that the real strength of the study may lie in the potential for pooling several similar studies. The problem will be discussed with reference to two examples of occupational cohort studies where differing prior information was available.

Adult↗
PubMed1992

Use of external rates in nested case-control studies with application to the international radiation study of cervical cancer patients.

A method is proposed for analysis of nested case-control studies that combines the matched comparison of covariate values between cases and controls and a comparison of the observed numbers of cases in the nesting cohort with expected numbers based on external rates and average relative risks estimated from the controls. The former comparison is based on the conditional likelihood for matched case-control studies and the latter on the unconditional likelihood for Poisson regression. It is shown that the two likelihoods are orthogonal and that their product is an estimator of the full survival likelihood that would have been obtained on the total cohort, had complete covariate data been available. Parameter estimation and significance tests follow in the usual way by maximizing this product likelihood. The method is illustrated using data on leukemia following irradiation for cervical cancer. In this study, the original cohort study showed a clear excess of leukemia in the first 15 years after exposure, but it was not feasible to obtain dose estimates on the entire cohort. However, the subsequent nested case-control study failed to demonstrate significant differences between alternative dose-response relations and effects of time-related modifiers. The combined analysis allows much clearer discrimination between alternative dose-time-response models.

Case-Control Studies↗
PubMed1991

Biased estimation of the odds ratio in case-control studies due to the use of ad hoc methods of correcting for missing values for confounding variables.

The effects of missing values for a confounding variable are investigated in the setting of case-control studies in which, for simplicity, the effect of one binary risk factor and one categoric confounding variable on disease risk is under investigation. Some ad hoc techniques with which to deal with missing values are examined under different assumptions about the missing-data mechanism. Examples are given to illustrate that the magnitude of the bias that is introduced by applying an inadequate procedure can be large under circumstances that occur frequently in empiric research. This is true even for so-called complete case analysis, i.e., when only data on subjects with complete information are used. Appropriate bias corrections are derived. Making use of data on those subjects who are neglected in complete case analysis by creating an additional category always results in biased estimation. An alternative is to allocate these subjects to the cells of the contingency table in an appropriate manner. This approach yields consistent estimates if the data are missing at random. Choosing an appropriate method for dealing with missing values always requires some knowledge of why the data are missing. This suggests that investigators should carry out validation studies to understand whether the missing values occur randomly across the study population or occur more frequently in specific subgroups.

Bias↗
PubMed1991

Radiation dose and leukaemia risk: general relative risk techniques for dose-response models in a matched case-control study.

Generalized relative risk functions were used to model radiation dose-response information from a large matched case-control study of leukaemia occurring after treatment for cervical cancer. Models suggested by radiobiological theory were investigated and compared to standard analyses of categorical dose-response to the linear model. Local radiation doses to each of fourteen bone marrow compartments for each patient were incorporated into the models, and the corresponding risks were summed. Conditional maximum likelihood methods were used to estimate risk parameters. Unique features of the analysis include modelling both induction and reduction of risk as a function of radiation dose absorbed by different parts of the body within individuals. Detailed statistical aspects of these analyses are presented and discussed.

Adult↗
PubMed1991

The evaluation of agreement by means of log-linear models: proxy interviews on reproductive history among floriculture workers in Colombia.

We used data from Colombia to compare responses from husbands and wives concerning the reproductive history of the women. We analyzed agreement in two ways: First, we compared kappa statistics between independent subgroups. Second, we evaluated agreement by means of log-linear models. Men underreported the total number of pregnancies and the number of abortions of their wives. Agreement on the term of the pregnancy was dependent on the ages of the partners. Log-linear modeling provides an attractive alternative to more usual ways of studying agreement.

Adolescent↗