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From |
Joseph Coveney <jcoveney@bigplanet.com> |

To |
Statalist <statalist@hsphsun2.harvard.edu> |

Subject |
Re: st: Sample size for equivalence trials in Stata |

Date |
Mon, 03 Oct 2005 20:44:47 +0900 |

Jannik Helweg-Larsen wrote (excerpted): There is also the artmenu ado (findit artmenu: SJ5-1 st0013_1. A menu-driven facility for complex sample size calculation randomized controlled trials with a survival or a binary update) which is supposed to provide non-inferiority sample size, however I haven't quite figured out how- the program does not seem accept two proportions of the same size.. The equivsize.ado by Philip Ryan is working very well- but should be limited in situations when proportions are less than 0.2- I wonder if other Stata based alternatives for calculating sample size exists for e.g. non-inferiority studies with small proportions (0.2)? -------------------------------------------------------------------------------- It seems that you wouldn't set the two proportions equal in using -artbin- for a noninferiority trial, but rather set one of the proportions equal to the assumed proportion of the reference treatment group and the other to the test group proportion that is just-detectable as inferior under the null hypothesis of inferiority. In the example given in -help artbinlg-, the reference group's proportion is 0.3 and the just-detectably worse performance of the test group is at 0.2, an odds ratio of 0.58 or so. Base upon off-the-cuff simulations below, you should be safe using -artbin- even with a reference group proportion of 10% and a just-detectable-inferior test proportion of 5% with odds ratio as the criterion. You'd need to check with Philip Ryan to be sure, but -equivsize- looks like it's based upon Blackwelder's* formula. It's not necessarily intended to be an endorsement of the practice, but a Web search turns up examples of sample size estimation based upon the Blackwelder formula with proportions smaller than 0.2 (larger than 0.8). Joseph Coveney *W. C. Blackwelder, Proving the null hypothesis in clinical trials. _Controlled Clinical Trials_ 3:345-53, 1982. program define arttest, rclass drop _all local 1 = `1' + mod(`1', 2) quietly { rndbin `1' `2' 1 compress generate byte group = _n > _N / 2 cs xb group, or /* woolf */ } return scalar lb_rd = r(lb_rd) return scalar lb_or = r(lb_or) end * set more off set seed0 `=date("2005-10-04", "ymd")' foreach proportion_pair in "0.05 0.1" "0.2 0.3" { artbin, pr(`proportion_pair') ngroups(2) /// aratios(1 1) distant(0) /// alpha(0.05) power(0.8) onesided(0) ni(1) tokenize `"`r(altp)'"', parse(", ") local rd = `1' - `3' local or = `1' / (1 - `1') / (`3' / (1 - `3')) simulate lb_rd = r(lb_rd) lb_or = r(lb_or), /// reps(10000) nodots: arttest `r(n)' `3' generate byte is_noninferior_rd = lb_rd > `rd' generate byte is_noninferior_or = lb_or > `or' assert !mi(is_noninferior_or) & !mi(is_noninferior_rd) summarize is_noninferior_* } exit * * 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/

**Follow-Ups**:**Re: st: Sample size for equivalence trials in Stata***From:*Philip Ryan <philip.ryan@adelaide.edu.au>

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