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st: RE: summ, format


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: summ, format
Date   Mon, 7 Jul 2003 20:26:11 +0100

SJ Friederich, Economics
> 
> A simple question in principle about the -format- option of 
> -summarize-: 
> from the online help, "format requests that the summary 
> statistics be 
> displayed using the display format associated with the 
> variables rather 
> than the default g display format."
> 
> Yet:
> 
> . g int edate = mdy(m,d,1900+y)
> 
> . l edate in 1
> 
>      +-------+
>      | edate |
>      |-------|
>   1. | 13163 |
>      +-------+
> 
> . format edate %d
> 
> . l edate in 1
> 
>      +-----------+
>      |     edate |
>      |-----------|
>   1. | 15jan1996 |
>      +-----------+
> 
> 
> . sum edate
> 
>     Variable |       Obs        Mean    Std. Dev.       Min 
>        Max
> -------------+----------------------------------------------
> ----------
>        edate |   5243770    13243.04    48.59888      13163 
>      13328
> 
> 
> . sum edate, format
> 
>     Variable |       Obs        Mean    Std. Dev.       Min 
>        Max
> -------------+----------------------------------------------
> ----------
>        edate |   5243770    13243.04    48.59888      13163 
>      13328
> 
> 
> The output is exactly the same. Does the option not work, or I am 
> misunderstanding how it operates?

There is, in effect, an extra rule not stated 
here: date formats are ignored by -summarize-.
Why? One can only guess:  

1. Perhaps the developers just thought it unlikely 
that people really wanted that, or never got round 
to implementing it. 

2. Also, a problem with date formats is that it is not 
obvious that the date format should be followed 
for all statistics. I guess that a user might want 
the mean, min, max etc. to be given as dates, 
but not the standard deviation, but is that 
correct. The variance of dates would 
have rather strange units. Skewness and kurtosis 
naturally have no units. 

3. Another awkward problem is this: would there be 
enough space in the -summarize, detail- display? 

I guess 1. is the key. 

-codebook- pays some attention to date formats, 
as I recall. 

On SSC, see -datesum-, -summdate-, perhaps others. 
(The -findit- database doesn't show SSC materials
at this instant.) 

Nick 
n.j.cox@durham.ac.uk 
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