 For calculating sample size of mean, that is a number among the single group, the formula is z square alpha into standard deviation square divided by d square. z alpha is the standard normal deviate, z alpha square will be 3.84, and standard deviation, we get it from the previous studies or from the pilot study. d is allowable error or precision. Here is one example for calculation of mean in a single group. Suppose we are doing the mean hemoglobin among newly diagnosed lung cancer patients, then the previous study says nine gram as the mean, then standard deviation is two, then we substitute in the formula 3.84 into standard deviation square that is two into two, 0.5 is the precision, and based on that we calculated the sample size. If we decrease this precision, we get increased sample size. If we increase this precision, then we get decreased sample size. Based on our study needs availability, we can adjust this precision and get a desired sample size.