Johannes Kepler University of Linz, Austria The empirical distribution function (ecdf) is unbiased in the usual sense, but shows certain order bias. Pyke suggested discrete ecdf using expectations of order statistics. Piecewise constant optimal ecdf saves 200%/N of sample size N. Results are compared with linear interpolation for U(0, 1), which require up to sixfold shorter samples at the same accuracy. Key words: Unbiased, order statistics, approximation, optimal. Introduction Natural sciences search for regularities in the chaos of real world events at different levels of complexity. As a rule, the regularities become apparent after statistical analysis of noisy data. This defines the fundamental role of statistical science, which collects causally connected facts for subsequent quantitative analysis. There are two kinds of probabilistic interface between statistical analysis and empirical observations. In differential form this corresponds to histograms, and in integral form to the so-called sample distribution function or empirical distribution function (edf or ecdf in Matlab notation), c.f. Pugachev (1984), Feller (1971), Press, et al. (1992), Abramowitz & Stegun (1970), Cramer (1971), Gibbons & Chakraborti (2003). If histogram bins contain sufficiently big numbers of points, the usual concept of ecdf is more or less satisfactory. The focus of this paper is on short samples, where a histogram approach is not possible and an optimal integral approach is welcome. Consider i.i.d. sample X with N elements, numbered according to their appearance on the x-axis statistics, Gibbons & Chakraborti (2003). In X= [X