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From |
Nick Cox <njcoxstata@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: adjusting hazard ratios in st cox using offset |

Date |
Wed, 17 Oct 2012 23:31:06 +0100 |

Also check out -groups- from SSC. Nick On Wed, Oct 17, 2012 at 11:27 PM, Steve Samuels <sjsamuels@gmail.com> wrote: > I'll just add that a model with only "main effects" of the other > procedures is difficult to interpret and probably badly fitting. With > enough data, you could fit some two-way interactions. But I would > investigate first how many different combinations of procedures you do > have and form groups based on those. One way to start is. > > ******************************************************* egen combos = > group(proc_a proc_b proc_c proc_d proc_e) > ******************************************************* > > You might find, for example, that two of the procedures commonly or > rarely occur together. > > Steve > > /*You have an interesting problem, but your proposal is flawed. Consider > the following simplified table for two procedures: > > | proc_b > proc_a | 0 1 | Total > -----------+----------------------+---------- > 0 | . 5 | 5 > 1 | 5 6 | 11 > -----------+----------------------+---------- > Total | 5 11 | 16 > You would like your model results to look like this: > proc_A 1.0 > proc_B ? > > But this is impossible: with three groups you need two indicator > variables. Here is an example. > > You have to define what you mean by "effect of proc_B adjusted for > proc_A." My suggestion would be to partition the data into two groups, > those with procedure A and those without procedure A. > > Steve > > ***********Code Begins********************* > capture program drop _all > clear > input proc_a proc_b > 1 0 > 1 1 > 0 1 > 0 1 > 0 1 > 1 0 > 1 1 > 1 0 > 1 1 > 0 1 > 0 1 > 1 1 > 1 1 > 1 0 > 1 1 > 1 0 > end > // define 3 groups > gen g10 = proc_a==1 & proc_b==0 > gen g01 = proc_a==0 & proc_b==1 > gen g11 = proc_a==1 & proc_b==1 > set seed 5503211 > gen stime = max(_n + 5*runiform(),1) > > stset stime > stcox g10 g01 g11, nohr nolog //3 indicators "g11" dropped > stcox proc_a proc_b, nohr nolog // 2 indicators > stcox proc_b if proc_a==1, nohr nolog > // the following doesn't work with only 2 procedures > stcox proc_b if proc_a==0, nohr nolog > ************************************************ >> On Oct 16, 2012, at 12:31 AM, Will Schairer wrote: >> >> Hi all, >> >> I have a dataset of procedures multiple follow-up events with an outcome of >> a complication. There are a few procedures, proc_A, proc_B, proc_C, proc_D, >> proc_E, which are all 0 -no- or 1 -yes-. >> >> I'm trying to create an stcox model where the hazard ratios are in >> reference to one of the procedures. Normally it would be fine just to set >> "proc" = 1,2,3,4, or 5, and use the i.proc. However, in this data there can >> be multiple procedures occurring in each visit, so I can't set just one >> variable like stcox i.proc >> >> So, I have: >> var HR >> age >> gender >> proc_A 0.7 >> proc_B 1.2 >> proc_C 3.4 >> proc_D 3.2 >> proc_E 2.5 >> >> and I'd like to have: >> var HR >> age >> gender >> proc_A 1.0 >> proc_B ? >> proc_C ? >> proc_D ? >> proc_E ? >> >> so that the ?'s are relative to proc_A = 1.0. >> >> ok so my question is, can I use -stcox- age gender B C D E, offset(A) as a >> way to normalize the other procedures to A? I have not found a good >> detailed resource on offset, but my understanding is that it is an exposure >> adjustment, so in a sense I'd be adjusting for exposure to proc A with HR = >> 1.0. Or, is there another way to do this? >> > * > * 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/

**References**:**st: adjusting hazard ratios in st cox using offset***From:*Will Schairer <wschairer@gmail.com>

**Re: st: adjusting hazard ratios in st cox using offset***From:*Steve Samuels <sjsamuels@gmail.com>

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