How to examine the effects of preanalytical factors

How to examine the effects of preanalytical factors? XXX Nordic Congress in Clinical Biochemistry Copenhagen 15 -06 -06 Ulrik Gerdes Klinisk Biokemisk Laboratorium ∙ Center for Psykiatrisk Grundforskning ∙ Risskov 1

Suggestions (I) • Think of the task as a comparison of methods, and use statistical models that are developed for that purpose • Always include a procedure (method) that is either considered ‘state of the art’ and/or is your standard procedure • Design the study so that you can both examine the effects on bias (systematic differences) and variation • Eliminate (or minimize) irrelevant sources of variation • Increase the size of the study to increase the precision of the estimates of the effects • Study the effects over a range of measurement values for the biochemical variables in question 2

Suggestions (II) • Don’t use aggregated statistical test (i. e. p-values) to evaluate whether two procedures are comparable • Compare the observed differences with the quality goals you have set for the analytical method • Share your results with others! 3

Summary Randomize! Use plenty! Procedure A Patient/Sample Analysis Use dublicates or triplicates! Procedure B Evaluation Data analysis What are the effects compared to the quality goals for the analysis? Use a proper model! 4

Thank you for your attention! 5

Questions? 6