Establishment of MLPA reference probe quality by statistical analyses of results obtained from cohorts comprising unaffected and affected individuals, respectively. To ensure a normal distribution of the obtained data for the reference probes AFAP1Lb (A) and AFAP1La (B) in all analyzed cohorts, the z score and Q-Q plots were established based upon data from 48 unaffected individuals and 145 breast tumors (affected individuals). The z score based histograms and Q-Q plots for AFAP1Lb followed a normal distribution for both cohorts, and the reference probe was included in the study (A). Data obtained for the reference probe AFAP1La were not normally distributed as illustrated by the z score based histograms and the Q-Q plots for both cohorts. The probe was excluded from further studies (B).