Hi, More of a statistical question, I'm trying to understand the formulation of the one-sample two-sided Kolmogorov-Smirnov statistic in stats::ks.test(), testing against a uniform distribution. Basically, it boils down to: x <- rnorm(100) n <- length(x) z <- punif(sort(x)) - (0:(n - 1)) / n max(z, 1 / n - z) which is equivalent to the textbook definition n <- length(x) z <- punif(sort(x)) Dplus <- max(sapply(1:n, function(i) i / n - z[i])) Dminus <- max(sapply(1:n, function(i) z[i] - (i - 1) / n)) max(Dplus, Dminus) (See, e.g., http://www.itl.nist.gov/div898/handbook/eda/section3/eda35g.htm, and Durbin (1971) ``Distribution theory for tests based on the sample distribution function'', p. 6) Why does the definition of Dminus have an i-1 in the numerator instead of i? I have a hunch it's got to do with right-continuity of the ecdf, but perhaps someone can shed some light on it. Thanks, Gad -- Gad Abraham MEng Student, Dept. CSSE and NICTA The University of Melbourne Parkville 3010, Victoria, Australia email: gabraham at csse.unimelb.edu.au web: http://www.csse.unimelb.edu.au/~gabraham