Dear Dr. Snow, Thank you for your reply. 1. Are you doing the 2 sample KS test? Comparing if 2 samples come from the same distribution? -Yes, I am doing 2-sample KS test 2. With 3,000 points you will still likely have power to find meaningless differences, what exactly are you trying to accomplish by doing the comparison? - I am comparing the swimming parameters of fish larvae such as move duration and move length. - The comparison is between treatments. -Sample sizes for example in one comparison pair : Control (2700 data pts) vs Medium (3012 pts) Dmax = 0.07 p-level <0.001 - Are there criteria to know if the differences are meaningless or not? 3. I am really only familiar with the KS test done in R (which did not make your list, yet you are asking on an R mailing list). Differences could be due to errors, different assumptions, different algorithms, sunspots, or any number of other things. Are the differences meaningful? R lets you see exactly what it is doing so you can check errors/assumptions/algorithms, I don't know about the ones you show. - sorry i forgot to list the R. I thought wessa.net was using R already. but I also made the software comparisons using R. The results were: with equal data points: results are the same in both Dmax and p-value with unequal data points : conclusions from results were the same such that significant difference between samples holds through using different softwares. Only the Dmax and p-values differ a bit. (please see attached file for the comparisons). 4. You will need to ask someone who knows the programs you reference to determine what input they are expecting. R expects the raw data. - Thanks! I expected this also. Thank you. -Rommel ----- Ursprüngliche Nachricht ----- Von: "Greg Snow-2 [via R]" <[email protected]> Datum: Samstag, 24. September 2011, 12:52 am Betreff: Re: Kolmogorov-Smirnov test An: rommel <[email protected]> Are you doing the 2 sample KS test? Comparing if 2 samples come from the same distribution? With 3,000 points you will still likely have power to find meaningless differences, what exactly are you trying to accomplish by doing the comparison? I am really only familiar with the KS test done in R (which did not make your list, yet you are asking on an R mailing list). Differences could be due to errors, different assumptions, different algorithms, sunspots, or any number of other things. Are the differences meaningful? R lets you see exactly what it is doing so you can check errors/assumptions/algorithms, I don't know about the ones you show. You will need to ask someone who knows the programs you reference to determine what input they are expecting. R expects the raw data. -----Original Message----- From: [hidden email] [mailto: [hidden email] ] On Behalf Of rommel Sent: Friday, September 23, 2011 7:51 AM To: [hidden email] Subject: Re: [R] Kolmogorov-Smirnov test Dear Dr. Snow, I would like to ask for help on my three questions regarding Kolmogorov Smirnov test. 1. 'With a sample size over 10,000 you will have power to detect differences that are not practically meaningful. ' -Is sample size of 3000 for each sample okay for using Kolmogorov Smirnov test? 2. I am checking whether my KS procedure is correct. I have compared results of KS tests using the following 3 softwares: 1. Statistica 2. http://www.wessa.net/rwasp_Reddy-Moores%20K-S%20Test.wasp 3. http://www.physics.csbsju.edu/stats/KS-test.html I have observed that the three softwares produced the same results only if the samples sizes are equal. However, when samples are not equal, I did not get similar results particularly from the wessa.net calculator. Is it allowed to do a KS test to compare samples with unequal sizes? 3. Is it allowed to use the raw data values in doing KS test? Or should I use the frequencies obtained from frequency distribution table of the raw data from each sample? I think that when I use the frequency, the KS test will construct new cumulative fractions from the frequencies, which I think is not right. Hope you can assist me. Thanks! -rommel -- View this message in context: http://r.789695.n4.nabble.com/Kolmogorov-Smirnov-test-tp3479506p3836910.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
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