Sample Size Calculation in Various Medical Research

Background: Sample size is the backbone of a scientific study/research in any field of science. It is mandatory at time of preparing proposal for a particular study. Large sample size is not needed and it is unethical also. Similarly, very too smaller sample is also. Materials and Methods: The adequate sample would be calculated either manually by using some formulae or using some existing statistical software like Statistical Package for Social Sciences (SPSS), Epi Info or online software with some conditions related to that study/research. Results: Previously existing literatures are not available then; sample size is to be determined based on pilot study in that region. In this article discuss about the sample size, its calculations, determine sample size we have to follow the conditions, knowledge to be needed at the time of calculating sample size, how much statistical power fix to a study, sample size and ethics, type-I and type-II errors, interpreting results of larger and smaller samples. Conclusion: From this article, I have concluded that a researcher has to write the proposal for his/her studies, find the appropriate parent/key article, finding the risk factors related to your studies, and the final step is to find the sample size with the help of a statistical expert. Then only proceed the study by the researchers. Keywords: sample size, proposal, statistical power, hypotheses, type-I and type-II errors, medical research