Reference change values and power functions.
Repeated samplings and measurements in the monitoring of patients to look for changes are common clinical problems. The "reference change value", calculated as zp x [2 x (CVI2 + CVA2)](1/2), where zp is the z-statistic and CVI and CVA 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 of missing significant changes in serial results from individuals (probability of false-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.
Iglesias Canadell
Natàlia
N
Laboratoris Clínics, Hospital General Universitari Vall d'Hebron, Barcelona, Spain. iglesias@hg.vhebron.es
Hyltoft Petersen
Per
P
Jensen
Esther
E
Ricós
Carmen
C
Jørgensen
Per E
PE
D000704:Analysis of Variance; D002118:Calcium / Q000097:blood*; D003404:Creatinine / Q000097:blood*; D003627:Data Interpretation, Statistical; D005189:False Positive Reactions; D006441:Hemoglobin A / Q000032:analysis*; D006801:Humans; D008954:Models, Biological; D011237:Predictive Value of Tests; D011336:Probability; D012016:Reference Values
D006441:Hemoglobin A; D003404:Creatinine; D002118:Calcium