What is the difference between confidence limits and expanded uncertainty?
In reporting measurement results, the combined uncertainty and its degrees of freedom can be used to establish a numerical interval that contains the true value with some confidence or probability. Confidence limits are computed assuming that the uncertainty estimate is for a combined error that follows either the normal (infinite degrees of freedom) or Student’s t distribution (finite degrees of freedom). Expanded uncertainties provide an approximate confidence limit, in which a coverage factor of k = 2 is used in place of the t-statistic. Expanded uncertainties are computed assuming a combined uncertainty estimate with infinite degrees of freedom for a combined error that is normally distributed.
