An alternative to the effective number of degrees of freedom

 In order to calculate the expanded uncertainty when one or more of the components of the standard uncertainty is based on a small number of degrees of freedom, the ISO Guide recommends utilising the 'effective number of degrees of freedom'. Calculating and utilising the 'effective number of degrees of freedom' to obtain a confidence interval both depend upon approximations, which, however, are adequate for determining an expanded uncertainty. This paper puts forward an alternative and simpler approximation which is also adequate but which is much easier to apply than the multi-step process given in the ISO Guide. Received: 2 July 1998 · Accepted: 12 August 1998