An apparatus for identifying outliers among chemical reaction assays, the apparatus comprising a transition point finder, configured to find at least one transition point in a cumulative function, the cumulative function giving a quantitative indication based on a count of points in a calculated space as a function of distance from a function dividing the calculated space into at least two groups, each one of the points representing results of a respective assay of a chemical reaction. The apparatus further comprises an outlier identifier, in communication with the transition point finder, configured to use a distance of the found transition point from the function dividing the calculated space, as a threshold, for identifying an outlier among the chemical reaction assays.