Exclude slopes that are exactly -1 I have to disagree since on page 711 of the 1983 paper it has reported: "Identical pairs of measurements with... do not contribute to the estimation of beta" ... For reasons of symmetry (see appendix)any Sij with a value of -1 is also disregared. Then, on the following 712 page the values of Sij with Sij <-1 are exluded since the number of the Sij (slope) <-1 is considered as an offset for calculating the "shifted median b of Sij" It is difficult to see the calculations since your function are very compact and I am not able to see their operation. By the way this fact is not even mentioned in the Medcalc Web site of the Passing and Bablok regression. I would like to ask you the following question: which is the greatest number of X and Y values that your macro can manage. Many thanks