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From | "Dr. Yu Chen" <profyuchen@gmail.com> |
To | statalist@hsphsun2.harvard.edu |
Subject | Re: st: bug in -xtile- |
Date | Fri, 1 Feb 2013 16:20:38 -0600 |
Hi, Xiao Yang, thank you so much for your quick response. Best, -- Yu Chen, Ph.D. Assistant Professor of Accounting A. R. Sanchez, Jr. School of Business, WHTC 218D Texas A&M International University 5201 University Boulevard Laredo, Texas 78041-1900 USA 956-326-2513 (office) 956-326-2479 (fax) On Fri, Feb 1, 2013 at 3:47 PM, Xiao Yang, StataCorp <xyang@stata.com> wrote: > > Yu Chen <profyuchen@gmail.com> encountered a bug in the way the -xtile- > command handles the case of the number of observations being less than the > requested number of quantiles. When the -if- condition is specified, > -xtile- > produces results. When the corresponding observations are dropped, > -xtile- > reports an error. > > > I think there is a bug in -xtile-. I ran the code below, and I still > > got deciles, but they are incomplete. I would expect missing values > > because there are not enough observations. > > > > sysuse auto,clear > > keep in 1/10 > > xtile decile=price if price<5000, nq(10) > > ... > > > > In other words, in the first example I added an if condition, and in > > the second example, I deleted those observations. Why is the result > > different? I think this is an inconsistency in -xtile-. > > > > sysuse auto,clear > > keep in 1/10 > > drop if price<5000 > > xtile decile=price , nq(10) > > > Nick Cox <njcoxstata@gmail.com> identified the problem in the -xtile- > command: > > > The code for -xtile- includes the test > > > > if `nquanti' > _N + 1 { > > di in red "nquantiles() must be less than or " /* > > */ "equal to number of observations plus one" > > exit 198 > > } > > > > but a better test would be something like > > > > marksample touse > > qui count if `touse' > > > > if `nquanti' > r(N) + 1 { > > > > The total number of observations _N is not the right number to check > > against. > > > This is indeed a bug. We will fix this in a future update. > > > -- Xiao > xyang@stata.com > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/faqs/resources/statalist-faq/ > * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/