Abstract
Sample size determination is one of the central tenets of medical research. If the sample size is inadequate, then the study will fail to detect a real difference between the effects of two clinical approaches. On the contrary, if the sample size is larger than what is needed, the study will become cumbersome and ethically prohibitive. Apart from this, the study will become expensive, time consuming and will have no added advantages. A study which needs a large sample size to prove any significant difference in two treatments must ensure the appropriate sample size. It is better to terminate such a study when the required sample size cannot be attained so that the funds and manpower can be conserved. When dealing with multiple sub-groups in a population the sample size should be increased the adequate level for each sub-group. To ensure the reliability of final comparison of the result, the significant level and power must be fixed before the sample size determination. Sample size determination is very important and always a difficult process to handle. It requires the collaboration of a specialist who has good scientific knowledge in the art and practice of medical statistics. A few suggestions are made in this paper regarding the methods to determine an optimum sample size in descriptive and analytical studies.Key Words: Sample size; Power analysis; Medical researchDOI: 10.3126/nje.v1i1.4100Nepal Journal of Epidemiology 2010;1 (1):4-10
Highlights
In Medical research, it is important to determine a sample size sufficient enough to ensure reliable conclusions
Sample size determination is very important and always a difficult process to handle. It requires the collaboration of a specialist who has good scientific knowledge in the art and practice of medical statistics
Sample size determination is an important issue in medical research but availability of literature in this topic is scanty
Summary
In Medical research, it is important to determine a sample size sufficient enough to ensure reliable conclusions. If the study is well designed with a desired sample size the standard error will be less and the power and precision will be good. Inferential statistics has two parts: estimation of population parameter and testing of hypothesis. The estimation method is used in prevalence/descriptive studies and the testing of hypothesis is used for cohort/case control/clinical trials. Correctness of whatever values or any relationship or association between variables derived from estimation can be verified. These are the two requirements for the analysis of data in medical research. Sample size determination Choosing a sample size is to be done by combination of logistical and pragmatic considerations which include: (a) The number of subjects who can be recruited in the given time period within available resources, and (b) The final figure calculated must represent the minimum number of subjects required to procure a reliable answer to the research question
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