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From |
jpitblado@stata.com (Jeff Pitblado, StataCorp LP) |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Prefix commands and returned matrix results |

Date |
Tue, 27 May 2008 12:01:03 -0500 |

Roger Newson <r.newson@imperial.ac.uk> asks to questions about Stata's prefix estimation commands. I'll address Roger's questions in reverse order. Question 2 ---------- Roger notes that -svy brr- doesn't currently work with -rclass- commands: > Another query concerns the svy brr prefix. This seems to be able to > access only e() results, and not r() results. Is this indeed the case? > And is it by accident or by design? And, if it is by accident, then are > there plans to fix it? This is definitely an accident. We have determined why -svy brr- isn't working properly with -rclass- commands. -svy jackknife- has a similar problem. Both of these commands will be fixed in a future ado-file update. Question 1 ---------- Rogers first question relates to working with matrix results other than regression coefficients and their standard errors (-_b- and -_se-): > I have a query about Stata prefix commands (such as bootstrap:, statsby: > and svy brr:) and returned matrix results. Based on the online help > accessible by typing > > whelp exp_list > > there does not seem to be any way in which an expression list used by a > prefix command can access elements of returned matrix results from the > command that has been prefixed, except for the estimates stored in e(b) > and the standard errors extracted from the diagonal of e(V). Is this > indeed the case? And, if you want the numeric results from a command to > be available to bootstrap:, statsby: and similar prefixes, do you have > to return them in scalars? I ask because I have 2 commands cendif and > censlope, which are part of the SSC package somersd, and they return > confidence intervals for percentile slopes, differences or ratios in a > matrix returned result r(cimat), in which the first column contains > percents, the second column contains the estimates, and the third and > fourth columns contain the lower and upper confidence limits, > respectively. If I want users to be able to bootstrap: or statsby: these > commands, accessing entries of those matrices, then must I also store > these entries in scalars, similar to the r(c_#) results returned by the > centile command in official Stata? While -_b- and -_se- are the only syntax elements in -exp_list- for conveniently dealing with elements from the matrices -e(b)- and -e(V)-, Stata's -el()- matrix function can be used to pull elements from other matrices; even other matrices in -r()- or -e()-. Here is a simple example using Roger's -cendif- command: . set seed 12345 . sysuse auto . bootstrap diff=el(r(cimat),1,2) : cendif mpg, by(for) --Jeff jpitblado@stata.com * * 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/

**Follow-Ups**:**RE: st: Prefix commands and returned matrix results***From:*"Newson, Roger B" <r.newson@imperial.ac.uk>

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