Dear people, OK, everyone, you win! Here is a summary of the Rayleigh Distribution information I received. I’ve not yet had time to dig through the references, but I'm sure multiples of them will work. I have not been able to digest any of this, sorry. Well, at least one person assured me I spelled the name right :) What _is_ the Rayleigh Distribution? Rayleigh distribution: "used mainly in engineering applications to denote a special form of the Weibull distribution [with beta=2]. It arises as the distribution of the miss distances from the target when the coordinates of the point of impact have the circular normal distribution with the center as its target." It's black body radiation distribution if energy is continuous not quantized, the one overturned by Planck. Most decent texts on the Gamma or Weibull will mention this Density , f(x)=(x/b^2)*exp(-x^2/(2b^2)) Cum. Distn, F(x)=1-exp(-x^2/(2b^2)) , b>0, x>0 mean b*sqrt(pi/2) mode b variance (2-pi/2)*b^2 When b = 1 it becomes a Chi-squared distribution with 2 d.f. One may include a displacement factor, a, in there: F(x)=1-exp-[(x-a)/b]^2 for x>a ------------------- Where to find it? The references - most are books, the next to last is a web site, and the last is a paper. Otherwise, in author order: Author Title Publisher Year Bury, Karl V Statistical Models in Applied Science Wiley. 1975 Evans, Hastings and Peacock Statistical Distributions Second ed., (p 134) Wiley, New York, 1993 Freund and Williams Dictionary and Basic Outline of Statistics, Dover Goodman, J. W., Statistical Optics John Wiley and Sons, New York, 1985 Johnson, Kotz and Balakrishnan compendia Johnson, N. L., & Kotz, S. Continuous distributions in statistics.(Vol. 2). Continuous Univariate Distributions, Vol. I. Boston: Houghton Mifflin Co. 1 970 Marriott F.H.C., A dictionary of statistical terms, 5th Ed Longman (1999 or 1990) Cambridge Dictionary of Statistics Best Fit manual Palisade, www.palisade.com Tuthill, T. A., Sperry, R. H., and Parker, K. J. Deviation from Rayleigh statistics in ultrasonic speckle Ultrasonic Imaging 10, 81--90 1988 ------------------- Who knows about it? Many thanks to the following who provided more than I thought possible: Dietrich Alte, Don W Brown, Nick Cox, Joe Haas, Tony Johnson, Miland Joshi, Diana Kornbrot, Peter M Lee, Roger Owen, Dave Stewardson. Apologies to any I missed. Gratefully, Jay -- Jay Warner Principal Scientist Warner Consulting, Inc. 4444 North Green Bay Road Racine, WI 53404-1216 USA Ph: (262) 634-9100 FAX: (262) 681-1133 email: [log in to unmask] web: http://www.a2q.com The A2Q Method (tm). What do you want to improve today? %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%