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Natàlia Iglesias Canadell, Per Hyltoft Petersen, Esther Jensen, Carmen Ricós, Per E. Jørgensen

Reference change values and power functions

Repeated samplings and measurements in the monitoring ofpatients to look for changes are common clinical problems. The “reference change value”, calculated as z_P×[2×(CV_I² + CV_A²)]^1/2, where z_P is the z-statistic and CV_I and CV_A are within-subject and analytical coefficients of variation, respectively, has been used to detect whether a measured difference between measurements is statistically significant. However, a reference change value only detects the probability of false-positives (type I error), and for this reason, a model to calculate the risk ofmissing significant changes in serial results from individuals (probability off alse-negatives) is investigated in this work by means of power functions. Therefore, when an analyte is being monitored in a patient, power functions estimate the probability of detecting a defined real change by measuring the difference. Thus, when a measured difference is the same as the calculated reference change value, then it will be detected in only 50% of situations.

Clinical Chemical Laboratory Medicine, Walter de Gruyter

Print ISSN: 1434-6621
Volume: 42, 04/2004
Pages: 415 - 422

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