This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
Standard error of mean in a population is calculated by the formula: 
Select and explain. 
A. SD/n, B. SD/mean, C. SD/[?]n, D. Mean/SD
C: SD/[?]n
Answer: C: SD/[?]n 
Explanation: Although the sampling distribution of the mean is approximately normally distributed, the sampling distributions of most other statistics are not. Therefore the population standard detion is estimated by the sample standard detion SD, and the SD is used in place of the population value in the calculation of the standard error; that is, the standard error in the population is estimated by, Ref: (2004). Chapter 4. Probability & Related Topics for Making Inferences About Data. In Dawson B, Trapp R.G. (Eds), Basic & Clinical Biostatistics, 4e.