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      How to Calculate Sample Size for Different Study Designs in Medical Research?


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          Calculation of exact sample size is an important part of research design. It is very important to understand that different study design need different method of sample size calculation and one formula cannot be used in all designs. In this short review we tried to educate researcher regarding various method of sample size calculation available for different study designs. In this review sample size calculation for most frequently used study designs are mentioned. For genetic and microbiological studies readers are requested to read other sources.

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          Most cited references12

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          Guidelines for the design and statistical analysis of experiments using laboratory animals.

          For ethical and economic reasons, it is important to design animal experiments well, to analyze the data correctly, and to use the minimum number of animals necessary to achieve the scientific objectives---but not so few as to miss biologically important effects or require unnecessary repetition of experiments. Investigators are urged to consult a statistician at the design stage and are reminded that no experiment should ever be started without a clear idea of how the resulting data are to be analyzed. These guidelines are provided to help biomedical research workers perform their experiments efficiently and analyze their results so that they can extract all useful information from the resulting data. Among the topics discussed are the varying purposes of experiments (e.g., exploratory vs. confirmatory); the experimental unit; the necessity of recording full experimental details (e.g., species, sex, age, microbiological status, strain and source of animals, and husbandry conditions); assigning experimental units to treatments using randomization; other aspects of the experiment (e.g., timing of measurements); using formal experimental designs (e.g., completely randomized and randomized block); estimating the size of the experiment using power and sample size calculations; screening raw data for obvious errors; using the t-test or analysis of variance for parametric analysis; and effective design of graphical data.
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            Sample size/power calculation for case-cohort studies.

            In epidemiologic studies and disease prevention trials, interest often involves estimation of the relationship between some disease endpoints and individual exposure. In some studies, due to the rarity of the disease and the cost in collecting the exposure information for the entire cohort, a case-cohort design, which consists of a small random sample of the whole cohort and all the diseased subjects, is often used. Previous work has focused on analyzing data from the case-cohort design and few have discussed the sample size issues. In this article, we describe two tests for the case-cohort design, which can be treated as a natural generalization of log-rank test in the full cohort design. We derive an explicit form for power/sample size calculation based on these two tests. A number of simulation studies have been used to illustrate the efficiency of the tests for the case-cohort design. An example is provided on how to use the formula.
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              Sample size calculation in epidemiological studies.


                Author and article information

                Indian J Psychol Med
                Indian J Psychol Med
                Indian Journal of Psychological Medicine
                Medknow Publications & Media Pvt Ltd (India )
                Apr-Jun 2013
                : 35
                : 2
                : 121-126
                [1]Department of Pharmacology, Govt. Medical College, Surat, Gujarat, India
                [1 ]Independent Researcher, Kolkata, West Bengal, India
                Author notes
                Address for correspondence: Dr. Jaykaran Charan, Department of Pharmacology, Govt. Medical College, Surat, Gujarat, India. E-mail: drjaykaran@ 123456yahoo.co.in
                Copyright: © Indian Journal of Psychological Medicine

                This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Review Article

                Clinical Psychology & Psychiatry
                medical research,sample size,study designs
                Clinical Psychology & Psychiatry
                medical research, sample size, study designs


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