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From |
"Siyam,AA (pgr)" <A.A.Siyam@lse.ac.uk> |

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

Subject |
st: RE: RE: RE: RE: RE: Bootstrapping and t-tests |

Date |
Wed, 12 Jun 2002 19:09:11 +0100 |

My thanks to Nick Winter, and pardon me for mis-typing your name. I have no missing values at all, I felt with such a small size sample (Obs=26) I could do better by presenting the conventional 95% C.I. for the mean-difference and a bootstrapped (bias-corrected) one. You are absolutely right, I could have used "summarize" or "ci" for that matter. Many thanks for your help. Amani -----Original Message----- From: Nick Winter [mailto:nwinter@policystudies.com] Sent: 12 June 2002 18:59 To: statalist@hsphsun2.harvard.edu Subject: st: RE: RE: RE: RE: Bootstrapping and t-tests > Ok, thanks to Nick Winters, I have learned something new By the way, it is "Winter" -- no "s" -- a pet peeve of mine. > Warning: Since ttest is not an estimation command or does > not set e(sample), bs has no way to determine > which observations are used in calculating the > statistics and so assumes that all observations > are used. This means no observations will be > excluded from the resampling due to missing values > or other reasons. > If the assumption is not true, press Break, save > the data, and drop the observations that are to > be excluded. Be sure the dataset in memory > contains only the relevant data. On the substance, the warning means that you must ensure there are no missing observations on your diff variable. You can do this by typing . count if diff==. If there are any, you should drop those observations before running your bootstrap: . preserve . drop if diff==. <<run bootstrap>> . restore By the way, you could just use the -summarize- command, rather than the -ttest-, if all you want is the mean. Nick Winter * * 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/ * * 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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