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From |
Nigel Perkins <nigel@ausvet.com.au> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: pkequiv and p-values from one-sided t-tests |

Date |
Mon, 25 Feb 2013 16:28:11 +1000 |

I am using pkequiv in Stata 12.1 to analyse data for bioequivalence . pkequiv value treat period sequence id, tost Classic confidence interval for bioequivalence ---------------------------------------------------------------------- [equivalence limits] [ test limits ] ---------------------------------------------------------------------- difference: -86.775 86.775 -150.067 185.817 ratio: 80% 120% 65.412% 142.827% ---------------------------------------------------------------------- probability test limits are within equivalence limits = 0.0160 Schuirmann's two one-sided tests ---------------------------------------------------------------------- upper test statistic = -0.797 p-value = 0.456 lower test statistic = 1.211 p-value = 0.271 Everything makes sense to me except the reported p-values for the Schuirmann's tests. The DF for this dataset is equal to 6 based on a 2-period cross-over study with n=4 in each sequence. The reported p-values appear to be two-sided p-values and not one-sided p-values. I can estimate one-sided p-values using Excel or a web-calculator and they are numerically equal to half the p-values reported by pkequiv. I expected the Schuirmann tests to each report a one-sided p-value. I have repeated this analysis using a couple of different datasets and the results appear to be consistent. I am wondering if I am doing something wrong here. Any comment would be much appreciated. Nigel Perkins AusVet, Australia nigel@ausvet.com.au * * 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/

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