Abstract
This paper presents a procedure for measuring a quantity when there is serially correlated data. In this situation, the statistical method of determining the standard uncertainty that assumes independence is inaccurate and, usually, anti-conservative. The procedure presented here involves calculating (a) an alternative estimate of the standard deviation of the sample mean for use as the standard uncertainty and (b) an associated number of degrees of freedom. Simulations for large and small samples show the procedure to substantially improve on the method that assumes independence, with the amount of improvement increasing with sample size.