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From |
jpitblado@stata.com (Jeff Pitblado, StataCorp LP) |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: stumped with lincom after svymean |

Date |
Tue, 31 Aug 2004 11:16:56 -0500 |

"Robert Bozick" <robertbozick@hotmail.com> asks about using -test- after -svymean, by()-: > Here is what I am trying to accomplish. I have a continuous variable y, and > a categorical variable x. The categorical variable x has three categories: > 0, 1, and 2. I want to test whether y is different among the categories of > my variable x. My data are collected using a stratfied, cluster design and > therefore I must use the survey commands. > > In previous versions of stata, I would use the code: > > svymean y, by(x) > svytest [x]0=[x]1 > > Stata 8 says that svytest no longer exists and that I should use the lincom > command. Maybe the coffee hasn't set in, but I cannot figure out how to do > replicate the above code using the lincom command based on the information > from Stata's help screen. > > So my question is two-fold: > 1 - How do I test group differences using the svy command in Stata 8 based > on my above example? > 2 - Is it possible to estimate a one-way anova to detect group differences > with svy commands in Stata 8 based on my above example? Here is an example using the auto data (not that I remove the labels so that my example appears closer the one above): . sysuse auto, clear . label drop _all . svyset, srs . svymean mpg, by(foreign) . test [mpg]0 = [mpg]1 When the -by()- option is supplied to -svymean-, the name of the variable that we are taking the mean of becomes something like an equation identifier when used with -test-. The values of the categories in the -by()- variable are used to identify which mean we are talking about. Here is the output from the above example: ***** BEGIN: . sysuse auto, clear (1978 Automobile Data) . label drop _all . svyset, srs simple random sample (SRS) . svymean mpg, by(foreign) Survey mean estimation pweight: <none> Number of obs = 74 Strata: <one> Number of strata = 1 PSU: <observations> Number of PSUs = 74 Population size = 74 ------------------------------------------------------------------------------ Mean Subpop. | Estimate Std. Err. [95% Conf. Interval] Deff ---------------+-------------------------------------------------------------- mpg | foreign==0 | 19.82692 .6558681 18.51978 21.13407 1 foreign==1 | 24.77273 1.386503 22.00943 27.53602 1 ------------------------------------------------------------------------------ . test [mpg]0 = [mpg]1 Adjusted Wald test ( 1) [mpg]0 - [mpg]1 = 0 F( 1, 73) = 10.40 Prob > F = 0.0019 ***** END: --Jeff jpitblado@stata.com * * 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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