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From |
Austin Nichols <austinnichols@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Testing whether two estimated survey means are statistically different |

Date |
Thu, 20 Oct 2011 10:39:10 -0400 |

Nick-- The poster (Andrew Wade) has survey data, though. In survey data, using a cluster-robust variance estimator, the two are identical. webuse nhanes2, clear svy: reg bpsystol black, sformat(%7.6f) qui svy: mean bpsystol, over(black) lincom _b[1]-_b[0], sformat(%7.6f) On Thu, Oct 20, 2011 at 10:00 AM, Nick Winter <nwinter@virginia.edu> wrote: > There is a subtle difference between -svy: reg- and -svy: mean- followed by > -lincom-. The former corresponds to a t-test with the assumption that the > variances in the two populations are equal; the latter corresponds (almost > exactly) to a t-test without that assumption. The "almost exactly" is due > to a difference in calculation of degrees of freedom. > > Leaving aside -svy-, we can see the slightly different standard errors: > > sysuse auto > reg mpg foreign > ttest mpg, over(foreign) > > mean: mpg, over(foreign) > lincom _b[Domestic]-_b[Foreign] > ttest mpg, over(foreign) unequal > > > - Nick Winter > > On 10/20/2011 4:58 AM, Maarten Buis wrote: >> >> On Wed, Oct 19, 2011 at 11:33 PM, Andrew Wade<awade@allenconsult.com.au> >> wrote: >>> >>> Presumably the regression approach, where you have a single dummy for the >>> sub-population, will be identical (or near identical) to: >>> - estimating svy: mean with over command (ie. mean for sub-population, >>> and not in sub-population). >>> - lincom after svy: mean. * * 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/

**Follow-Ups**:**Re: st: Testing whether two estimated survey means are statistically different***From:*Nick Winter <nwinter@virginia.edu>

**References**:**Re: st: Testing whether two estimated survey means are statistically different***From:*"Andrew Wade" <awade@allenconsult.com.au>

**Re: st: Testing whether two estimated survey means are statistically different***From:*Maarten Buis <maartenlbuis@gmail.com>

**Re: st: Testing whether two estimated survey means are statistically different***From:*Nick Winter <nwinter@virginia.edu>

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