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

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

Subject |
RE: st: Generate a new variable [four firm concentration ratio] |

Date |
Mon, 21 Nov 2005 23:57:22 -0000 |

The line within the loop should be replace firstfour = firstfour + s`i' if s`i' >= 0 Nick n.j.cox@durham.ac.uk > -----Original Message----- > From: owner-statalist@hsphsun2.harvard.edu > [mailto:owner-statalist@hsphsun2.harvard.edu]On Behalf Of Nick Cox > Sent: 21 November 2005 23:55 > To: statalist@hsphsun2.harvard.edu > Subject: RE: st: Generate a new variable [four firm > concentration ratio] > > > I think I follow some of this, although I cannot > reproduce the capricious behaviour you seem > to imply here. I would like to see a copy of > (a subset of) your data that apparently produces > this problem. Strictly, it implies a bug in Stata's > -numlist- command, which does the sorting here. > > The help for -rowsort- indicates that missing values > are allowed. If you sort seven values, some of which > are missing, the missing values will not disappear! > (Or did you expect they would?) Following usual Stata > rules they will be sorted to high values. > > You are correct that this then will not be what you want. > > One way round this is to use -mvencode- to map > missings to some negative number, say -999, presuming > that is not a legitimate number of consumers. These > will always sort lower than any legitimate number. > Then the sum of the first four firms should trap > any -999. However, if any of the first four firms > is missing, and so mapped to -999, then the concentration > ratio should presumably be 100%. > > drop s1-s7 > mvencode F?mt, mv(-999) > rowsort F?_mt, gen(s1-s7) descend > > replace firstfour = 0 > forval i = 1/4 { > replace firstfour = s`i' if s`i' >= 0 > } > replace firstfour = 100 * firstfour / CONSUM_mt > > mvdecode F?mt, mv(-999) > > Nick > n.j.cox@durham.ac.uk > > ALICE DOBSON > > > Thanks Nick. It works selectively as I am not getting > > "firstfour" for all > > rows. > > This is probably because the rows have values for one to > > seven firms and not > > for all seven firms > > Further, I checked the data editor and see that in such cases > > where the data > > is avaiable for less than seven firms the command arranges > > the top four > > values s1-s4 (arbitrarily) in columns for say s3-s6 > > Hence, I do not get firstfour for all such cases > > > >From: n j cox <n.j.cox@durham.ac.uk> > > >Reply-To: statalist@hsphsun2.harvard.edu > > >To: statalist@hsphsun2.harvard.edu > > >Subject: Re: st: Generate a new variable [four firm > > concentration ratio] > > >Date: Mon, 21 Nov 2005 21:31:19 +0000 > > > > > >If the number of consumers is integer, then > > >just install -rowsort- from SSC. > > > > > >rowsort F?_mt, gen(s1-s7) descend > > >gen firstfour = 100 * (s1 + s2 + s3 + s4) / CONSUM_mt > > > > > >Nick > > >n.j.cox@durham.ac.uk > > > > > >ALICE DOBSON > > > > > >I use stata 9.1 > > > > > >I have an unbalanced panel data of the type: > > > > > >geographical region (m = 1..1154) > > >year (t = 1..7) > > > > > >with the following variables: > > > > > >total number of consumers in each region (CONSUM_mt) > > >total number of consumers of seven firms in each region > > (F1_mt, F2_mt, > > >F3_mt, F4_mt, F5_mt, F6_mt, F7_mt) > > > > > > > > >I want to calculate the four firm concentration ratio for > > each region, > > >C4_mt, which is the proportion of the number of consumers of > > top four firms > > >to the total number of consumers in that region, in percentage > > > > > >Could anyone be kind enough to help me with this simple > calculation? > > > > > >GEOGREGN YEAR CONSUM F1 F2 F3 F4 F5 F6 F7 C4 > > >M1 1969 > > >M1 1970 > > >M1 1971 > > >M1 1972 > > >M1 1973 > > >M1 1974 > > >M1 1975 > > >M2 1969 > > >M2 1970 > > >M2 1971 > > >M2 1972 > > >. > > >. > > * > * 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/ > * * 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/

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