Articles: prospective-studies.
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In this article we provide an overview of the different study designs commonly utilized in carrying out clinical and public health research and of the points to consider in reviewing these study designs. The design and conduct of cross-sectional health surveys, case-control, prospective, and case-crossover observational studies, and randomized controlled trials, are discussed in this review article. It is hoped that careful attention to the concerns we have raised will lead to the design and conduct of high-quality research projects and their write-up.
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Epidemiologic reviews · Jan 1998
ReviewExposure measurement in cohort studies: the challenges of prospective data collection.
Cohort study designs have several advantages over case-control studies in terms of exposure measurement. If exposure measurement occurs before disease occurrence, cohort studies are much less prone to differential measurement error. Prospective data collection should also reduce measurement error due to poor recall of past exposures. ⋯ Long-term cohort studies which cover the etiologically relevant time period could improve the accuracy of measures of exposures by use of repeated biologic measures or repeated updates of self-reported exposures. Measurement error also can be reduced by judicious choice of a cohort to study and by careful attention to quality control procedures. Continued emphasis on the evaluation and improvement of the measurement properties of instruments used in epidemiologic studies will improve the validity of the results of cohort studies.
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If the relative effectiveness of different treatments that might be used in clinical practice is to be evaluated reliably, it is very important that the evaluation is carried out in an appropriate manner. This is especially true where the differences between treatments are expected to be moderate, and so easily obscured by the play of chance or systematic bias. Although such differences are often of considerable clinical importance, they can be difficult to assess and require a large amount of randomized evidence. ⋯ This approach requires considerable time and effort. However, it will add to the analyses that can be performed and will remove many of the problems associated with a reliance on published data alone and some of the problems that can arise from the use of aggregate data. This paper sets out some of the reasons for this and some of the techniques used for individual patient data-based meta-analysis.
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Bull. World Health Organ. · Jan 1994
ReviewNutritional status as a predictor of child survival: summarizing the association and quantifying its global impact.
By pooling the results from five previously published prospective studies, we have obtained estimates of the relative risks of mortality among young children 6-24 months after they had been identified as having mild-to-moderate or severe malnutrition. These risk estimates, along with global malnutrition prevalence data, were then used to calculate the total number of young-childhood deaths "attributable" to malnutrition in developing countries. Young children (6-60 months of age) with mild-to-moderate malnutrition (60-80% of the median weight-for-age of the reference population) had 2.2 times the risk of dying during the follow-up period than their better nourished counterparts (> 80% of the median reference weight-for-age). ⋯ Each year approximately 2.3 million deaths of young children in developing countries (41% of the total for this age group) are associated with malnutrition. The comparability of studies, methods used to derive pooled values, potentially confounding factors that may influence risk estimates, and the validity of the results are discussed. Child survival programmes should assign greater priority to the control of childhood malnutrition.
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The evidence for and against the association of oral contraceptives (OCs) with vascular disease is reviewed, along with the possible pathophysiologic mechanisms for such an association, including effects on coagulation, circulating lipoproteins, and glucose metabolism. The new, low-dose estrogen OCs appear to affect coagulation minimally, and anticoagulant as well as procoagulant effects have been documented. Such concomitant factors as cigarette smoking, obesity, a family history of thrombosis, lack of physical activity, and blood type influence coagulation more strongly. ⋯ However, educating patients in the management of breakthrough bleeding can help reduce the number of women who must be switched to higher-dose OCs. Epidemiologic evidence confirms the safety of low-dose OCs. By selecting patients carefully, the risk of vascular disease from oral contraception can be reduced to very low levels.