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From |
n j cox <n.j.cox@durham.ac.uk> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: computing means and quantiles for groups using weights |

Date |
Mon, 16 Jul 2007 19:47:16 +0100 |

Paolo Naticchioni asked something like this on various occasions:

-------------------------------------------------------------------

I want to create a new variable including the means for some groups

(strata) of the population.

For instance, assume my strata are year, gender, education.

Using egen I can compute the average of some outcome variable, for

instance wage, using the following:

bysort year gender education: egen average=mean(wage)

However, using egen I cannot use any types of weights. I would like to

use weights (weights with average 1). Do you know how can I introduce

weights in a easy way? Probably it is very easy, but I do not know the

command.

I would like also to compute some quantile of the distribution, like

the 10th quantile, the median, the 90th percentile, etc.

Also in this case, I can use egen

bysort year gender education: egen p90=pctile(wage), p(90)

However, also in this case it is not possible to use weights, the

consider the weighted distribution.

---------------------------------------------------------------------

Paolo is correct. -egen-, as documented by StataCorp, does not support weights. I guess there are three possible reasons:

1. StataCorp started out with a relatively simple syntax for

-egen- and never saw grounds for/never got round to complicating

it.

2. -egen- is a wrapper for a call to some -egen- function. In

general, some functions could sensibly be called with weights

and some not. -egen- as such has no way of knowing which is which.

That leaves the responsibility for coping with weights to individual

functions. It's messy to have the innermost function do most of the

checking and the extent of that is best reduced.

3. Something else I haven't thought of.

No matter. There are user-written -egen- functions on SSC that do what you want. Weights are just specified in a non-standard way, via options. David Kantor's -_gwtmean- is a package with a weighted mean function for -egen-. Ulrich Kohler's function -wpctile()- is in the

-egenmore- package.

If they didn't exist, other solutions are possible, but I will not

spell any out at this point.

Nick

n.j.cox@durham.ac.uk

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**Follow-Ups**:**Re: st: computing means and quantiles for groups using weights***From:*"Paolo Naticchioni" <paonat.stata@gmail.com>

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