Coverage intervals according to MARLAP, Bayesian statistics and the new ISO 11929 for ionising radiation measurements

The coverage intervals stipulated by ISO 11929 (2010) for estimating the uncertainty from ionising radiation measurements of replicate samples are compared with those of MARLAP (=Multi-Agency Radiological Laboratory Analytical Protocols Manual) and of Bayesian statistics. The latter two intervals agree well despite their different concepts. Whereas for either of them the ratio of the length of the coverage interval and MARLAP's standard uncertainty grows when the number of samples decreases, no such growth arises for the interval mandated by ISO 11929 (2010). It may therefore be too short (e.g. for three samples by a factor of approximately 2).

► Study of coverage intervals stipulated by the new standard ISO 11929 (2010).
► Focus is on radiation measurements of replicate samples with extra-Poisson variation.
► In this situation the intervals of MARLAP (GUM) and Bayesian statistics are similar.
► But those of ISO 11929 may be too short, e.g. for 3 samples by a factor of about 2.
► ISO 11929 disregards statistical uncertainty, which the other two approaches consider.