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# Re: st: geometric means

 From Abu Camara To statalist@hsphsun2.harvard.edu Subject Re: st: geometric means Date Wed, 12 Jun 2013 18:21:59 +0300

```Hi Nick,

On 12 June 2013 10:34, Nick Cox <njcoxstata@gmail.com> wrote:
> There's an -egen- function -gmean()- in -egenmore- (SSC), but the
> problem  yields also to elementary mathematics and official Stata:
>
> sysuse auto
> egen gmean = mean(ln(mpg)), by(rep78)
> replace gmean = exp(gmean)
>
> Note that you can't take this further and go
>
> egen gmean2 = exp(mean(ln(mpg))), by(rep78)
>
> because -egen- expects to see an -egen- function on the right-hand
> size and -exp()- is not an -egen- function. Why then is the first code
> OK? Because the -egen- function -mean()- can work on an expression and
> a call to a Stata function is fine.
>
> The overloading of the word "function" needs a little care here.
> -egen- functions are those documented under -egen-. Stata functions
> are documented under -functions-. There is sometimes scope to use
> Stata functions _inside_ calls to -egen- functions, as here. -egen-
> functions cannot be used outside -egen- in any circumstances.
>
> Nick
> njcoxstata@gmail.com
>
>
> On 11 June 2013 12:42, Nick Cox <njcoxstata@gmail.com> wrote:
>> Check out -egen-.
>>
>> Nick
>>
>>
>> On 11 Jun 2013, at 10:35, Abu Camara <abucamara@gmail.com> wrote:
>>
>>> Hi Stata list,
>>>
>>> I want to compute geometric means by year (time series)  for a list of
>>> countries with Stata's "ameans" command.
>>> BY and OVER are not supported by ameans.
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--
Best Wishes,
Abu Camara
*
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```