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From |
"Tiago V. Pereira" <tiago.pereira@mbe.bio.br> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: Why does -centile- provide different results compared to -sum- or -pctile-? |

Date |
Sat, 17 Jul 2010 02:11:21 -0300 (BRT) |

Thanks to Peter as well, that's exactly the explanation I was looking for! Tiago ------------------ Thanks, Martin! So, are both correct in statistical terms? Sorry for taking your time for such apparently "easy-to-find" questions. Our Stata is institutional, and we don't have access to the manuals at the lab. All the best, Tiago Dear statalister, Am I misinterpreting the outpus or there is something wrong with -centile-? For example, the values for percentile 10 differ in -centile- (89.666) compard to -sum- and -pctile- (90.66666). Cheers! Tiago (Stata 9 and 10.1 provide identical results). */ -------- start do --------- clear input X 223 104.3333 198.3333 126 95 101.3333 133 90.66666 38 91 101 36.5 101 203 92.5 149 142.3333 89.33334 105.6667 123.3333 136 240.6667 162.3333 98.66666 181.6667 261 206 251 339.3333 219.3333 114 end sum X, detail centile X , centile(1 5 10 25 50 75 90 95 99) _pctile X, nq(10) dis "P10 = " r(r1) dis "P90 = " r(r9) */ ---------end do ----------------- My outputs: sum X, detail X ------------------------------------------------------------- Percentiles Smallest 1% 36.5 36.5 5% 38 38 10% 90.66666 89.33334 Obs 31 25% 98.66666 90.66666 Sum of Wgt. 31 50% 126 Mean 146.914 Largest Std. Dev. 69.5917 75% 203 240.6667 90% 240.6667 251 Variance 4843.005 95% 261 261 Skewness .7895009 99% 339.3333 339.3333 Kurtosis 3.214935 . . centile X , centile(1 5 10 25 50 75 90 95 99) -- Binom. Interp. -- Variable | Obs Percentile Centile [95% Conf. Interval] -------------+------------------------------------------------------------- X | 31 1 36.5 36.5 57.78294* | 5 37.4 36.5 90.95187* | 10 89.60001 36.5 95.97249* | 25 98.66666 90.32367 107.523 | 50 126 101.1658 172.048 | 75 203 140.9225 243.3249 | 90 248.9333 205.2043 339.3333* | 95 292.3333 225.5506 339.3333* | 99 339.3333 257.1462 339.3333* * Lower (upper) confidence limit held at minimum (maximum) of sample . . _pctile X, nq(10) . . dis "P10 = " r(r1) P10 = 90.666656 . dis "P90 = " r(r9) P90 = 240.6667 -- Tiago V. Pereira, MSc, PhD Center for Studies of the Human Genome Department of Genetics and Evolutionary Biology University of São Paulo, Rua do Matão, 277 São Paulo - SP CEP 05508-900 * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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