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From |
Maarten buis <maartenbuis@yahoo.co.uk> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: calculating means by group, with weights |

Date |
Wed, 25 Jun 2008 17:45:38 +0100 (BST) |

--- Gisella Young <gisellayoung@yahoo.com> wrote: > I am trying to calculate the mean of a variable ("income") across > groups ("bracket"), but using the relevant survey weights (variable > "weight"). I tried saying: > > bys bracket: egen float meanincome = mean(income) [fweight=weight] > > but this is not possible since the egen command does not allow for > weighting. This is a problem for me as if I do not use the weights > the means will be wrong. Since you are using fweiths there are at least 2 strategies you could follow. The first is that fweights tell you how many observations a record represents. You can turn your data into unweighted data by -expand-ing it, this way each record stands for 1 observation, and there is no need to weight. See -help expand- and the example below. The other option is to use -collapse- to make a new dataset with weighted means, and -merge- that back into your original data. See -help collapse- and -help merge-. As can be seen in the example below, the two methods yield exactly the same result (as it should). *------------- begin example ----------------- sysuse auto, clear tempfile a b sort rep78 save `a' collapse (mean) meanmpg=mpg [fw=tru], by(rep78) sort rep78 save `b' use `a', clear merge rep78 using `b' expand tru bys rep78 : egen meanmpg2 = mean(mpg) tab meanmpg meanmpg2 *-------------- end example ------------------- (For more on how to use examples I sent to the Statalist, see http://home.fsw.vu.nl/m.buis/stata/exampleFAQ.html ) Hope this helps, Maarten ----------------------------------------- Maarten L. Buis Department of Social Research Methodology Vrije Universiteit Amsterdam Boelelaan 1081 1081 HV Amsterdam The Netherlands visiting address: Buitenveldertselaan 3 (Metropolitan), room Z434 +31 20 5986715 http://home.fsw.vu.nl/m.buis/ ----------------------------------------- __________________________________________________________ Sent from Yahoo! Mail. A Smarter Email http://uk.docs.yahoo.com/nowyoucan.html * * 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/

**References**:**st: calculating means by group, with weights***From:*Gisella Young <gisellayoung@yahoo.com>

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