![]() ![]() Laboratory conditions cannot always be directly transferred to normal clinical practice and processes in isolated cells or in animals are not equivalent to those in man (= generalizability) ( 2).īasic research also includes the development and improvement of analytical procedures-such as analytical determination of enzymes, markers or genes-, imaging procedures-such as computed tomography or magnetic resonance imaging-, and gene sequencing-such as the link between eye color and specific gene sequences. External validity is a more difficult issue. High internal validity (= unambiguity) is achieved by setting up standardized experimental conditions, with low variability in the units of observation (for example, cells, animals or materials). In experiments, specific hypotheses are investigated and causal statements are made. ![]() It is also important that confounding factors should be specifically controlled or reduced. ![]() ![]() For example, the population, number of groups, case numbers, treatments and dosages can be exactly specified. The procedure and the experimental design can be precisely specified and implemented ( 1). In almost all experiments, at least one independent variable is varied and the effects on the dependent variable are investigated. The article is based on a selective literature research on study types in medical research, as well as the authors’ own experience.īasic medical research (otherwise known as experimental research) includes animal experiments, cell studies, biochemical, genetic and physiological investigations, and studies on the properties of drugs and materials. The conception, implementation, advantages, disadvantages and possibilities of using the different study types are illustrated by examples. This article covers the classification of individual study types. A special article will be devoted to study types in secondary research, such as meta-analyses and reviews. The article focuses on study types in primary research. If the wrong study type has been selected, this cannot be rectified once the study has started.Īfter an earlier publication dealing with aspects of study design, the present article deals with study types in primary and secondary research. The study type is determined by the question to be answered and decides how useful a scientific study is and how well it can be interpreted. The study type is a component of the study design (see the article "Study Design in Medical Research") and must be specified before the study starts. The quality, reliability and possibility of publishing a study are decisively influenced by the selection of a proper study design. ![]()
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