Academy of Medical Sciences of I.R. Iran Archives of Iranian Medicine 1029-2977 16 5 2013 05 01 Sample Size Calculation for Epidemiologic Studies: Principles and Methods 0 0 EN Farin Kamangar Farhad Islami Journal Article This paper discusses the statistical principles, methods, and software programs used to calculate sample size. In addition, it reviews the practical challenges faced in calculating sample size. We show that because of such challenges, statistical calculations often do not provide us with a clear-cut number for the study sample size; rather they suggest a range of reasonable numbers. The paper also discusses several important nonstatistical considerations in determination of sample size, such as novelty of the study and availability of resources.