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

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: by and missing values question |

Date |
Mon, 11 May 2009 11:00:03 +0100 |

Question [3] is easiest to answer: excluding missing values is an automatic effect of following -marksample touse- with commands that work -if `touse'. Question [1] has unhelpful and helpful answers. As your command cycles over the categories of the varlist fed to -by:- each set of results is returned, but then immediately afterwards overwritten by the next set. So all you can see afterwards with -return list- is the last set of results. This was an important reason for StataCorp to add -statsby-. There are other solutions too, but involving different programming styles. Question [2] is a good question. You could engineer your program so that it always returned total results too, but the effect would inevitably be that it did that every time round the loop. In practice I'd tend to issue the command twice, once without and once with -by:-. A very small detail: In qui su `dif' if `touse' [`weight'`exp'] , meanonly the -quietly- is redundant, as -summarize, meanonly- never produces output in the results window (at most error messages). It does no harm, naturally. Nick n.j.cox@durham.ac.uk Nikolaos Kanellopoulos I have written the following very simple program cap pr drop logdiff program define logdiff , rclass byable(recall) syntax varlist(min=2 max=2) [if] [in] [fweight aweight] version 8.0 tempvar dif marksample touse qui count local N = r(N) qui count if `touse' if r(N) == 0 error 2000 local n = r(N) qui gen `dif' = (`n'/`N')*abs(ln(`2') - ln(`1')) if `touse' qui su `dif' if `touse' [`weight'`exp'] , meanonly loc diff = r(mean) di as text "Log Difference: " as result `diff' return scalar diff = `diff' return local N = `N' return local n = `n' end My questions are: [1] How can I return the results for all categories when I use the by option and not only for the last category? [2] How can I display and return the results for the total of a category when I use the by option? i.e. return the same results as without the by option. [3] How can I exclude the missing values from my estimations both when I use and not use the by option? * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**st: RE: RE: by and missing values question***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

**References**:**st: by and missing values question***From:*Nikolaos Kanellopoulos <nkkanel@yahoo.gr>

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