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From |
"Paul Seed" <P.T.Seed@qmul.ac.uk> |

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

Subject |
st: RE: statalist-digest V4 #970 |

Date |
Thu, 8 Aug 2002 13:42:51 +0100 |

Many thanks to Gary for this. Changing the saved result to a scalar did indeed take care of the problem. Although the term "control" is used, this is not a matched case-control study, rather a comparison of two groups of pregnant women, (with & without APS). An unpaied t-test (or non-parametric equivalent) is entirely appropriate. Date: Wed, 07 Aug 2002 10:47:41 -0700 From: Gary Longton <glongton@fhcrc.org> Subject: Re: st: Problems with -bs- command Paul Seed wrote: > I am interested in a bootstrapped confidence interval for the > difference between two means, and to save time > wish to work out the means using -summ, meanonly-. > > I have written a Stata program to do this, which runs perfectly well > on it's own. However, when trying to get -bs- to work out the confidence > intervals, I get an unexplained error message. > > Any thoughts on wher ethe problem lies, greatly appreciated. the program: > cap prog drop myprog > prog define myprog, rclass > summ centile if aps, mean > di "r(mean) = " r(mean) > local m1 = r(mean) > return local m1 = r(mean) > summ centile if control, mean > return local m2 = r(mean) > return local m2_m1 = `m1' - r(mean) > end myprog called with -bs- > set seed 35435141 > bs "myprog" "r(m1)", reps(50) or > bs "myprog" "r(m1) r(m2) r(m2_m1)", reps(50) and output: > . * Now use it for bootstrap" > . set seed 35435141 > > . bs "myprog" "r(m1) r(m2) r(m2_m1)", reps(50) > > command: myprog > statistics: r(m1) r(m2) r(m2_m1) > error in statistic: r(m1) > r(198); I believe the -bs- command is complaining about the use of macro results placed in the expression list, i.e. "r(m1)" It should work if these are instead scalar results. Eg. in the program - -myprog-, replace return local m1 = r(mean) with return scalar m1 = r(mean) ^^^^^^ and likewise for m2, and m2_m1 and it should work. However, am wondering whether this type of sampling is best for your design? The command > summ centile if control, mean hints that this might be a case-control design?, in which case you might want to be sampling separately from cases and controls? which can be done, but not with - -bs-. - - Gary * * 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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