On Fri, Dec 18, 2009 at 1:38 PM, Ben Abbott <[email protected]> wrote: > > On Dec 18, 2009, at 1:40 AM, Bruce Axtens wrote: > >> I'm getting a weird answer from meandev as compared to Excel, Wolfram Alpha >> and Protium. >> >> GNU Octave, version 3.2.3 >> Octave was configured for "i686-pc-mingw32" >> >> meandev([8, 8, 9, 11, 11, 15, 16, 19, 19, 20, 20, 21, 21, 25, 32]) --> ans >> = 5.8571 >> >> All the others give 5.46667 >> e.g. WolframAlpha >> http://www.wolframalpha.com/input/?i=mean+deviation%288%2C+8%2C++9%2C+11%2C+11%2C+15%2C+16%2C+19%2C+19%2C+20%2C+20%2C+21%2C+21%2C+25%2C+32%29 >> >> What am I doing wrong? >> >> Kind regards, >> Bruce. > > Looking at the link below ... > > http://mathworld.wolfram.com/MeanDeviation.html > > ... the mean deviation may be calculated as ... > > meandev = @(x) mean (abs(x-mean(x))); > meandev([8, 8, 9, 11, 11, 15, 16, 19, 19, 20, 20, 21, 21, 25, 32]) > ans = 5.4667 > > So it does appear that you have found a bug. > > Unfortunately, you've reported this to the wrong mail list. > [email protected] is for Octave and its core functions. The function, > meandev, is part of the statistics package at Octave-Forge. The correct mail > list for that is [email protected]. > > I've removed [email protected] and added [email protected] to > the recipients. > > Ben > > >
It's not a bug, it's that meandev divides by n-1 rather than n. Maximum likelihood estimation calls for dividing by n. There is an option for unbiased estimation, too, which calls for dividing by n-1. octave:1> 5.46667*15/14 ans = 5.8571 octave:2> Cheers, Michael ------------------------------------------------------------------------------ This SF.Net email is sponsored by the Verizon Developer Community Take advantage of Verizon's best-in-class app development support A streamlined, 14 day to market process makes app distribution fast and easy Join now and get one step closer to millions of Verizon customers http://p.sf.net/sfu/verizon-dev2dev _______________________________________________ Octave-dev mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/octave-dev
