Define particulars4/10/2023 Patient or disease registries are organised systems for the long-term collection of uniform data on a population that is defined by a particular disease, condition or exposure, with the purpose to study changes over time. Randomized controlled trial (RCT)-extension studies are informative because, due to RCT randomization, they are free from confounding by indication. infection, has occurred in each group is compared in a nested case-control study controls are drawn from a fully known cohort. In a case-control study a representative group of patients with a specific clinical feature is compared with controls, and the frequencies at which an external factor, e.g. Prospective cohort studies use (some) data that are not yet available at the time the research is conceived, whereas in retrospective studies the data already exist. diagnosis or specific treatment, by analyzing data acquired at various intervals. A cohort study is a longitudinal study that investigates patients with a defining characteristic, e.g. In ecological studies the unit of analysis is population or group, and relationships on patient level cannot be established. Cross-sectional studies, by simultaneously assessing clinical phenomena and external factors, enable the discovery and quantification of associations. Case reports and case series are usually based on accidental observations or routinely collected data. The term 'retrograde' is proposed to explicate that cross-sectional studies may obtain data that cover (long) preceding periods. Observational studies may be cross-sectional vs. Whether observational findings are demonstrative, indicative or only suggestive, depends on the research question, whether and how the design fits this question, analytical techniques, and the quality of data. Observational studies are well suited for making discoveries and assessing new explanations of phenomena, but less so for establishing causal relationships, due to confounding by indication (selection bias), co-morbidity, socio-economic or other factors. This paper presents an overview of the various observational designs and their applications in clinical studies. Observational studies investigate a wide range of topics in multiple sclerosis research.
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