Analysis of Key Comparison Data: Unstable Travelling Standards
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A procedure for the analysis of key comparison data is proposed in the case where the travelling standard shows a deterministic or random drift. It is assumed that some parametric model such as a linear trend is appropriate for modelling the deterministic part of the drift. The random part of the drift is assumed to be adequately described by a random walk model. The chosen drift model is determined by least squares and a model check is carried out. If the model check is satisfied, the derived drift model is applied to determine degrees of equivalence. A star-type sequence is required for the comparison in order to check the adequacy of the random drift model. The procedure is illustrated by its application to simulated data.
Key wordskey comparison stability random walk least squares
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