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From |
Stace Maples <[email protected]> |

To |
[email protected] |

Subject |
st: ksmirnov output in STATA question... |

Date |
Sun, 24 Jul 2005 17:58:21 -0700 (PDT) |

I have a question about interpretation of the ksmirnov statistic in STATA... I have a dataset that records a variable called VISPROM for an entire population (approx 190,000 observations), and of that population, I have several samples such as paleo (n=43), archaic (n=1026), anasazi (n=5412). I have created dummy variables for sorting, giving the sample the value of 0 and the population the value 1, so that when I sort on the dummy variable, my sample is the first value of, say, the dummy variable paleo, and my population is the second value of the dummy variable. Using the ksmirnov test, to compare the two samples as follows: ksmirnov visprom, by(paleo) I get the following result: . sort paleo . ksmirnov visprom, by(paleo) Two-sample Kolmogorov-Smirnov test for equality of distribution functions: Smaller group D P-value Corrected ---------------------------------------------- 0: 0.0000 1.000 1: -0.1509 0.177 Combined K-S: 0.1509 0.353 0.285 Now, according to my text (Stats in Geography, Ebdon), my critical value for D with DoF of 43, is .21 at a significance level of .05. Further, the book says that a KS D statistic that is GREATER than the critical value indicates that the Null Hyp that the distributions are equal can be rejected, and that there is evidence of a non-random pattern. I interpret the above STATA output as follows: The D statistic for paleo camopared with the population is .1509, which is less than the critical value of .21 for 43 degrees of freedom. Therefore, I cannot reject the null hypothesis that the sample and population distributions are equal at a significance level of .05. Does that sound right? What about the p-value of 1 for H0? What is the significance of the Corrected values (and what is the Combined)? I sure wish there was an annotated output for ksmirnov on the stata site. Here is another output that I REALLY don't know what to do with... . sort archaic . ksmirnov visprom, by(archaic) Two-sample Kolmogorov-Smirnov test for equality of distribution functions: Smaller group D P-value Corrected ---------------------------------------------- 0: 0.0631 0.000 1: -0.0645 0.000 Combined K-S: 0.0645 0.000 0.000 any help is appreciated In F,L&T, Stace D. Maples School of Social Sciences Office: GR 3.416 GIS Lab: GR 3.206 University of Texas at Dallas P.O. Box 830688 Richardson, TX 75083 Phone: (214) 641-0920 [email protected] www.stacemaples.com Office & Lab Hours: Monday 2:00pm - 6:00pm, Saturday 10:00am - noon GIS Lab: GR 3.206 or by appointment * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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