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| From | Nick Cox <njcoxstata@gmail.com> |
| To | statalist@hsphsun2.harvard.edu |
| Subject | Re: st: graphing estimates and confidence intervals |
| Date | Sun, 12 May 2013 13:16:41 +0100 |
Excellent point. On 10/05/2013, Alan Neustadtl <alan.neustadtl@gmail.com> wrote: > As usual, Nick Cox's canonical replies are tremendously useful to both > teach and remind us of how to approach a number of Stata problems. Thank > you for your comments. > > I add another approach using -marginsplot- as in the following example: > > sysuse auto > regress mpg i.for > margins i.for > marginsplot, recast(scatter) > > Best, > Alan > > On Fri, May 10, 2013 at 8:52 AM, Nick Cox <njcoxstata@gmail.com> wrote: >> Two recent threads both centred on graphical display of estimates >> together with confidence intervals: The start points were >> >> http://www.stata.com/statalist/archive/2013-05/msg00293.html >> >> http://www.stata.com/statalist/archive/2013-05/msg00310.html >> >> This post is intended mainly as a kind of broad-brush overview of the >> question. It also adds some detail omitted from those threads. In >> turn, naturally, please comment if I miss anything of importance or >> interest. >> >> The main idea is that while estimates can be plotted easily with >> -twoway scatter- or -graph dot- you are in practice going to find it >> difficult to show confidence intervals directly other than by -twoway >> rcap-. (It's only convention that might inhibit you from using -twoway >> rspike- instead.) It follows that you need to focus on using -twoway-. >> Bluntly, -graph dot- (or -graph bar- for those so inclined) is a dead >> end here. >> >> There are two broad strategies. >> >> 1. You can build your own command by assembling a composite -twoway- >> call using -scatter- for the point estimates and -rcap- for the >> intervals. This can be combined, with increasing difficulty, with >> showing different results for different groups on one or more levels. >> An example to explain levels here: using sex as a classifier gives one >> level and using race or region or both would add one or two more >> levels. >> >> With one level you will presumably just want to plot your grouping >> variable on one of the axes. >> >> With two or more levels, using -by()- is the easiest approach to add >> an extra level of classification, but just adding spacing can be as or >> more effective. Sometimes with -by()- there is too much scaffolding >> and too much loss of real estate. >> >> If you have any group variable that is string, things are easier if >> you -encode- it or use -egen, group()- to produce an equivalent >> numeric variable with value labels. >> >> 2. Alternatively, you can look for a command that does all that for >> you. The commands differ in whether they expect that you already have >> the estimates (point and interval) or they will undertake to do that >> calculation for you. The more standard the calculation, the more >> likely that a canned command already exists. >> >> -serrbar- is an old official command which doesn't do much but may >> match simple needs. My impression is that it is little known, but that >> may be because it is little mentioned, and that in turn because it is >> of little use. >> >> -dotplot- is an official command which supports display of mean +/- >> SD. It's worth knowing that, but it's unlikely to be what you want >> under this heading. >> >> -ciplot- is an oldish user-written command (SSC, Nick Cox). Its basic >> idea is to call up -ci- repeatedly and then plot the results. There is >> support for multiple groups and multiple variables. If it doesn't go >> as far as you want, the bad news is that I have no interest in >> developing it, but it's more flexible than any official command I can >> recall. For example, >> >> sysuse auto >> ciplot foreign , binomial jeffreys by(rep78) >> >> shows how you can reach through to -ci-. >> >> -stripplot- (SSC, Nick Cox) was mentioned in recent posts. Its display >> of confidence intervals is based on exactly the same idea as -ciplot-, >> to call up -ci- for the calculations. Its philosophy is to show the >> raw data too, although nothing beyond an ectoplasmic sense of my mild >> disapproval stops you suppressing the data display with e.g >> -ms(none)-. >> >> -eclplot- (SSC also SJ, Roger Newson) is another user-written command, >> and one characteristically well thought out, documented and >> maintained. It's not competing because it is focused on a different >> case, in which you already have estimates and confidence limits to >> hand; other programs of Roger's are of much help in assembling and >> analysing such results. >> >> I want to flag strongly the scope for using -statsby- in this >> territory, which I wrote up in >> >> SJ-10-1 gr0045 . . . . . . . . . . . . . Speaking Stata: The statsby >> strategy >> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N. J. >> Cox >> Q1/10 SJ 10(1):143--151 (no >> commands) >> demonstrates the use of statsby to prepare a reduced >> dataset for subsequent graphing >> >> .pdf freely available at >> http://www.stata-journal.com/sjpdf.html?articlenum=gr0045 >> >> Confidence intervals are a major example. (That paper was inspired by >> a single throw-away remark by Vince Wiggins. It was one of many >> occasions in which deciding to write about something made me aware of >> something in Stata I was underestimating.) >> >> I would also like to mention a general discussion of graphical technique >> in >> >> SJ-8-2 gr0034 . . . . . . . . . . Speaking Stata: Between tables and >> graphs >> (help labmask, seqvar if installed) . . . . . . . . . . . . N. J. >> Cox >> Q2/08 SJ 8(2):269--289 >> outlines techniques for producing table-like graphs >> >> .pdf freely available at >> http://www.stata-journal.com/sjpdf.html?articlenum=gr0034 >> >> Nick >> njcoxstata@gmail.com >> * >> * For searches and help try: >> * http://www.stata.com/help.cgi?search >> * http://www.stata.com/support/faqs/resources/statalist-faq/ >> * http://www.ats.ucla.edu/stat/stata/ > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/faqs/resources/statalist-faq/ > * http://www.ats.ucla.edu/stat/stata/ > -- Nick njcoxstata@gmail.com * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/