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In the debate about 'what is a competent general practitioner?' little attention has been paid ot the actual practice situation of general practitioners. This paper, based on the 18 most important studies in the literature about medical competence, tries to re-initiate this debate by proposing a clear distinction between 'competence', (what a physician is capable of doing) and 'performance' (what a physician does in his day-to-day practice). With this distinction we looked at whether studies defined both competence and performance, how they dealt with these concepts, what measurement instruments were used and what the conclusions of the studies were. Although it is the common reasoning that competence is a good predictor of performance this concept could not be affirmed. This survey shows that the majority of studies use wrong concepts and come to invalid conclusions. With the empirical distinction between competence and performance however, this paper proposes new directions for the quality assessment of general practitioners.

To study the association between dietary fiber, beta-carotene and breast cancer, the average daily intake of these dietary components was compared among 133 incident breast cancer cases and 238 population controls. Average daily intake of cereal products, fruit and vegetables was also studied. A statistically significant lower energy-adjusted intake of dietary fiber was observed in cases than in controls (mean +/- SD: 25.4 +/- 6.7 g vs. 27.7 +/- 7.4 g, 95% confidence interval (CI) of the age-adjusted difference = -3.8, -0.8). Intake of beta-carotene was similar for cases and controls. The multivariate adjusted odds ratio (OR) of breast cancer among women in the highest quartile of intake of cereal products, as compared to those in the lowest quartile, was 0.42 (95% CI = 0.19-0.92) and the trend was statistically significant (p = 0.03). The corresponding OR for intake of dietary fiber was 0.55 (95% CI = 0.26-1.17) but the trend was not significant. The OR for the highest quartile of intake of beta-carotene, fruit, vegetables, and all vegetable products combined was less than unity, but there was no significant inverse trend. These results suggest that a high intake of cereal products, especially those rich in fiber, may be inversely related to incidence of breast cancer.

Age-adjusted dietary fat intake of 133 incident Dutch breast cancer cases was significantly (p less than 0.01) higher than in 289 apparently healthy controls (mean and standard deviation: 102 +/- 36 g and 92 +/- 30 g, respectively). The age-adjusted relative odds of breast cancer showed a positive trend (p less than 0.05) with increasing fat intake. The multivariate adjusted relative odds was 3.5 (95% Cl = 1.6-7.6) for subjects in the highest quintile of fat intake (above 113 g) compared to those in the lowest quintile (below 65 g); this corresponds to a 30% increased risk per 10% of energy derived from fat. The association could not be attributed to energy intake, nor to the degree of saturation of the fat nor to any specific dietary source of fat.

In order to assess the variability among histopathologists in grading cervical dysplasia, four experienced histopathologists examined the same set of 106 biopsy specimens and assigned them to one of five diagnostic categories. These were: no dysplasia, mild dysplasia, moderate dysplasia, severe dysplasia and carcinoma in situ. The histopathologists did not discuss the grading criteria beforehand. There was considerable disagreement among the pathologists: unweighted group kappa 0.28, weighted group kappa 0.56. It appeared that all grades of dysplasia were equally difficult to distinguish from adjacent categories. Various explanations for this interobserver variation are put forward.

This case-control study was undertaken to determine whether exposure to organic solvents, as experienced by Dutch painters, causes an increased risk of disability due to neuropsychiatric disorders. Cases and controls were selected from the Dutch Painters' and Construction Workers' Organizations. Cases were defined as male persons receiving disability benefits due to neuropsychiatric disorders. The controls consisted of a random sample of 1000 male persons from the total study population. Cases (n = 252) and controls (n = 822) participated in our study by returning the completed questionnaires. The questionnaire was used to collect information about occupational history and the presence of potentially confounding factors. The adjusted Odds Ratio for the total group of neuropsychiatric disorders did not reach a statistically significant level (OR = 1.17; P less than 0.30). Although a stronger association was suggested between "neuroses" (ICD 300) and exposure to organic solvents (OR = 2.30; P less than 0.05), there are indications that this relationship is merely the result of classification bias. The results of this study do not confirm, but also do not completely exclude, that Dutch painters are at increased risk of being prematurely disabled due to neuropsychiatric disorders.

In 1986, a prospective cohort study on diet and cancer was started in The Netherlands. The cohort (n = 120, 852) of 55-69 year old men (48.2%) and women (51.8%) originates from 204 computerized municipal population registries. At baseline, participants completed a self-administered questionnaire on diet and potential confounding variables. In addition, about 67% of the participants provided toenail clippings. Cancer follow-up consists of record linkage to a pathology registry and to cancer registries. The initial interest is in stomach, colorectal, breast and lung tumors. A case-cohort approach is applied, in which detailed follow-up information of a random subcohort (n = 5000) provides an estimate of the person-time experience of the cohort. Exposure data of the subcohort will be combined with those of incident cases, yielding exposure-specific incidence rate ratios. The intraindividual variation in determinants is estimated by annually repeated measurements (n = 250) within the subcohort. The rationale, efficiency aspects and study characteristics are discussed.

Observations with respect to the relationship between symptoms and diseases can seriously be biased by selection phenomena. This selection may occur from the general population, via consultation behavior, diagnostic and therapeutic activities of the general practitioner, and by referral. Relationships may be suggested and reproduced even if they do not exist in unselected populations, as a product of diagnostic routines. Correction for selection bias can only be achieved by choosing proper comparison groups. While this can be done in a general practice setting, this is almost impossible after referral, as is demonstrated in this paper. Surprisingly, the most unbiased estimation of the relationship between symptoms and diseases after referral can be made from patient groups that are referred for reason unrelated to the disease under study. Definitive answers for the general practitioner can only be provided by prospective studies from a primary care setting. In the meantime, however, biased relationships can be maintained by teaching knowledge derived from a specialist experience.

A population of 379 Dutch workers exposed to organic solvents was compared with a non-exposed population of 443 workers with regard to the prevalence of prenarcotic and neuraesthenic symptoms. Participants completed a questionnaire to collect information about their occupational history, exposure to organic solvents, and the occurrence of symptoms. The results of the study indicated that workers exposed to solvents have a higher reporting rate of prenarcotic symptoms than workers not exposed to solvents. The prevalence of chronic neurotoxic effects, however, in the form of neuraesthenic symptoms was only weakly associated with reported exposure to organic solvents. The influence of work stress in the development of these symptoms is perhaps more important than the role of exposure to organic solvents. It is concluded that the organic solvent syndrome type I, as defined by an international workshop, is not an important health hazard among Dutch painters.

A study was conducted to investigate the existence of a "specific" neurotoxic effect due to long-term exposure to organic solvents. A comparison was made regarding diagnoses, symptoms and other relevant medical data between persons receiving a disability pension on the basis of a neuropsychiatric disorder selected from an exposed (painters) and non-exposed (construction workers) trade organization. Information was collected from their medical files at the occupational health department. Concerning diagnoses and symptoms, no significant differences were found between exposed and non-exposed patients. No indications were found for the existence of a "typical" complex of symptoms associated with exposure to organic solvents among painters in The Netherlands. The number of reported symptoms was not related to the duration of exposure, thus lending no support for a dose-effect relationship. If a neurotoxic effect does exist among Dutch painters, it is of a non-specific type and not clearly distinguishable from other mental disorders.

In collaboration with three pathology departments a case-control study was conducted in the southern part of the Netherlands to investigate the risk of gastric cancer in coal miners. Between 1 January 1973 and 31 December 1983, 323 male patients were diagnosed as having a malignant neoplasm of the stomach. For each case a control was selected from the same pathology department, matched on year of birth and regardless of diagnosis. The archives of the Central Coal Miners Pension Fund were searched to obtain information about whether or not a patient had ever worked for a coal mining company in the Netherlands. Twenty two per cent of the patients had been registered as an underground coal miner, compared with 20% of the control group (odds ratio of 1.14, 95% confidence interval: 0.33-1.73). Those with gastric cancer who had ever worked underground in a coal mine did so for an average period of 16.9 years compared with an average of 19.7 years in the control group. The study gives no indication that the underground workers of the Dutch coal mines had a raised risk of developing a malignant neoplasm of the stomach.

In a case-control study in The Netherlands, we observed a significantly lower consumption of fermented milk products (predominantly yogurt and buttermilk) among 133 incident breast cancer cases as compared to 289 population controls (mean +/- SD among users only, 116 +/- 100 versus 157 +/- 144 g/day; P less than 0.01). The age-adjusted odds ratio of daily consumption of 1.5 glasses (greater than or equal to 225 g) of fermented milk versus none was 0.50 (95% confidence interval, 0.23-1.08). When fermented milk was entered as a continuous variable (per g) in either age-adjusted or multivariate analysis, the odds ratio expressed per 225 g was 0.63 (multivariate-adjusted 95% confidence interval, 0.41-0.96). After multivariate adjustment for intake of fat and other confounders, a statistically significant decrease in breast cancer risk was also observed for increasing intake of Gouda cheese. The multivariate-adjusted odds ratio expressed per 60 g of this fermented product was 0.56 (95% confidence interval, 0.33-0.95). For daily intake of milk, no statistically significant differences were observed between cases and controls. These results support the hypothesis that high consumption of fermented milk products may protect against breast cancer.

Habitual alcohol consumption, in terms of dose and frequency, average daily intake, as well as drinking alcohol at age 25 were compared between 120 incident breast cancer cases and 164 population controls in The Netherlands. Dietary and lifestyle factors, past and present alcohol consumption were established in 1985-1987 in home interviews. In premenopausal women a protective effect of low alcohol consumption (1-4 g/day) as compared to non-drinkers was suggested. The multivariate adjusted odds ratio (OR) comparing women drinking greater than or equal to 30 g with women drinking 1 to 4 g alcohol daily was 8.5 (95% confidence interval: (Cl) = 1.1-65.1). The OR for a dose of alcohol of greater than or equal to 15 g versus 1-14 g was 4.0 (Cl = 1.0-15.6) and for drinking more versus less than three times a week the OR was 2.8 (Cl = 0.8-9.8). In post-menopausal women no association was observed between recent drinking habits and breast cancer risk. In these women, however, the adjusted OR for drinking alcohol before the age of 25 was 2.4 (Cl = 1.0-5.6). Although causal inference is hampered by the cultural aspects of drinking habits, the results suggest that moderate drinking does not increase risk. Drinking more than 30 g daily or a high dose may enhance risk in premenopausal women. Furthermore, an early start to drinking alcohol may increase the relative risk for breast cancer even beyond menopause.