SEM is usually estimated by the sample estimate of the population standard deviation ( sample standard deviation ) divided by the square root of the sample size ( assuming statistical independence of the values in the sample ) : where s is the sample standard deviation ( i.e. , the sample-based estimate of the standard deviation of the population ) , and n is the size ( number of observations ) of the sample .
where s is the sample standard deviation ( i.e. , the sample-based estimate of the standard deviation of the population ) , and n is the number of measurements in the sample .