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Consistent treatment of measurement bias, including the question of whether or not to correct for bias, is essential for the comparability of measurement results. The case for correcting for bias is discussed, and it is shown that instances in which bias is known or suspected, but in which a specific correction cannot be justified, are comparatively common. The ISO Guide to the Expression of Uncertainty in Measurement does not provide well for this situation. It is concluded that there is a need for guidance on handling cases of uncorrected bias. Several different published approaches to the treatment of uncorrected bias and its uncertainty are critically reviewed with regard to coverage probability and simplicity of execution. On the basis of current studies, and taking into account testing laboratory needs for a simple and consistent approach with a symmetric uncertainty interval, we conclude that for most cases with large degrees of freedom, linear addition of a bias term adjusted for exact coverage ("U(e)") as described by Synek is to be preferred. This approach does, however, become more complex if degrees of freedom are low. For modest bias and low degrees of freedom, summation of bias, bias uncertainty and observed value uncertainty in quadrature ("RSSu") provides a similar interval and is simpler to adapt to reduced degrees of freedom, at the cost of a more restricted range of application if accurate coverage is desired.

Out of 134 patients patch tested after total hip replacement (metal-toplastic) 13 were sensitive to one or two of the implanted metals. In a prospective series of 112 patients, nine were sensitive to nickel before and another three developed sensitivity to nickel or cobalt after the arthroplasty. In the retrospective as well as in the prospective series the complications could in all cases but one be explained on grounds other than allergy. The incidence of contact allergy to nickel before a planned arthroplasty was 12 per cent in females and 4 per cent i;l males. It is doubtful whether metal sensitivity could be induced by a total hip arthroplasty. However, in cases of a preexisting metal allergy, a certain degree of caution is recommended.