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

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: While/if for individual observations |

Date |
Thu, 21 Mar 2013 17:39:03 +0000 |

Thanks for the THANKS! 1. My code is fine. I could not have cited its results otherwise. The line l, sepby(ID) is a separate command. -l- means -list-. I guess the problem is merely that the lines got combined in your mailer. 2. This is easy. After bysort ID (visitdate) : gen spell = sum(start) you can go bysort ID spell (visitdate) : gen elapsed = visitdate - visitdate[1] If this is cryptic, a reading list includes a. The help for -by:-, which may be too concise as a tutorial. b. SJ-2-1 pr0004 . . . . . . . . . . Speaking Stata: How to move step by: step . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N. J. Cox Q1/02 SJ 2(1):86--102 (no commands) explains the use of the by varlist : construct to tackle a variety of problems with group structure, ranging from simple calculations for each of several groups to more advanced manipulations that use the built-in _n and _N .pdf at http://www.stata-journal.com/sjpdf.html?articlenum=pr0004 which may be too long-winded. c. -tsspell- (SSC) and its help file, because it looks as if you will be working with spells in the future. d. SJ-7-2 dm0029 . . . . . . . . . . . . . . Speaking Stata: Identifying spells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N. J. Cox Q2/07 SJ 7(2):249--265 (no commands) shows how to handle spells with complete control over spell specification .pdf at http://www.stata-journal.com/sjpdf.html?articlenum=dm0029 for the same reason. On Thu, Mar 21, 2013 at 4:49 PM, Williams, Barbara <Barbara.Williams@vmmc.org> wrote: > Nick- > THANK YOU! For your reply to my question. > (I needed to think about my problem in a new way) > This is what I need ALMOST. > > 2 things: > 1. The code that you sent does not work-- invalid "l" (I have Stata 12): > . gen visitdate = date(VisitDate, "DMY") > . format visitdate %td > . tsset ID visitdate > panel variable: ID (weakly balanced) > time variable: visitdate, 01feb2011 to 10oct2011, but with gaps > delta: 1 day > . capture ssc inst panelthin, replace > . panelthin, gen(start) min(28) > . bysort ID (visitdate) : gen spell = sum(start) l, sepby(ID) > invalid 'l' > r(198); > > 2. For each spell, I want number of elapsed days since the "start": > generate elapsedays = 0 if start ==1 > replace elapsedays = X if ??? > > Barb Williams > > -----Original Message----- > From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nick Cox > Sent: Thursday, March 21, 2013 5:07 > To: statalist@hsphsun2.harvard.edu > Subject: Re: st: While/if for individual observations > > I can't follow all of this, but I have some suggestions which should help. > > First off, a sufficient reason for your code to fail is that you cannot use subscripts in a -replace- statement, so that for example > > replace abxin28days[`i'] = 1 + abxin28days[`i'] > > would need to be > > replace abxin28days = 1 + abxin28days[`i'] in `i' > > except that the subscript is not needed and > > replace abxin28days = 1 + abxin28days in `i' > > would do fine. (Code like this suggests knowing a lot about other languages, which does not always help.) > > There is also some major confusion between local macros and variables, which are quite different beasts in Stata. > > Second, there are cases in which a loop over observations is needed, and > > SJ-7-3 pr0033 . . . . . . . . . . . . . . Stata tip 51: Events in intervals > . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N. J. Cox > Q3/07 SJ 7(3):440--443 (no commands) > tip for counting or summarizing irregularly spaced > events in intervals > > Free .pdf at http://www.stata-journal.com/article.html?article=pr0033 > > discusses technique for problems a bit like yours. However, I am not clear that you actually need such an approach here (but the ideas may help in other problems). > > Third, there are two kinds of manipulation bound together here, summarising antibiotic use and the idea that a lapse of 28 days implies a fresh start. I would rather take the second first, and here advertise -panelthin- (SSC) as addressing it. > > Fourth, I don't get what your calculation is with the antibiotics, and don't see where numbers such as 4 and 6 come from. But using -egen- with -by()- options might be your answer. I have given you a -spell- variable. > > Code so far > > clear > input ID str9 VisitDate Antibiotics_YN > 100 01feb2011 0 > 100 02feb2011 0 > 100 04feb2011 1 > 100 10may2011 1 > 100 10oct2011 1 > 101 01feb2011 0 > 101 12mar2011 0 > 101 13mar2011 0 > 101 14mar2011 0 > 101 18mar2011 1 > end > gen visitdate = date(VisitDate, "DMY") > format visitdate %td > tsset ID visitdate > capture ssc inst panelthin, replace > panelthin, gen(start) min(28) > bysort ID (visitdate) : gen spell = sum(start) l , sepby(ID) > > > +--------------------------------------------------------+ > | ID VisitDate Antibi~N visitdate start spell | > |--------------------------------------------------------| > 1. | 100 01feb2011 0 01feb2011 1 1 | > 2. | 100 02feb2011 0 02feb2011 0 1 | > 3. | 100 04feb2011 1 04feb2011 0 1 | > 4. | 100 10may2011 1 10may2011 1 2 | > 5. | 100 10oct2011 1 10oct2011 1 3 | > |--------------------------------------------------------| > 6. | 101 01feb2011 0 01feb2011 1 1 | > 7. | 101 12mar2011 0 12mar2011 1 2 | > 8. | 101 13mar2011 0 13mar2011 0 2 | > 9. | 101 14mar2011 0 14mar2011 0 2 | > 10. | 101 18mar2011 1 18mar2011 0 2 | > +--------------------------------------------------------+ > > > On Wed, Mar 20, 2013 at 7:10 PM, Williams, Barbara <Barbara.Williams@vmmc.org> wrote: >> My data: >> I have a list of 20,000+ patient visits to a clinic with the following 3 variables: >> >> ID VisitDate Antibiotics_YN >> 100 01feb2011 0 >> 100 02feb2011 0 >> 100 04feb2011 1 >> 100 10may2011 1 >> 100 10oct2011 1 >> 101 01feb2011 0 >> 101 12mar2011 0 >> 101 13mar2011 0 >> 101 14mar2011 0 >> 101 18mar2011 1 >> ... >> >> My question: >> I would like to create a new variable which labels Antibiotics WITHIN 28 days of their first visit. >> AND If the patient has another visit more than 28 days after the first visit, the time is re-set (new series). >> For ID=100 First series of visits beginning 01feb2011 Antibiotics on visitday = 4 >> Second series of visits beginning 10may2011 Antibiotics on visitday = 1 >> Third series of visits beginning 10oct2011 >> Antibiotics on visitday =1 For ID=101 First series of visits beginning 01feb2011 No antibiotics >> Second series of visits beginning 12mar2011 >> Antibiotics on visitday = 6 >> >> >> My syntax (doesn't run, I'm not sure how to do this): >> local i = 1 >> local N = _N >> while `i' <=`N' { >> local firstdate = VisitDate[`i'] >> while ID[`i'] == ID[`i' - 1] & VisitDate[`i'] <= firstdate + 28 { >> replace abxin28days[`i'] = 1 + abxin28days[`i'] >> local `i' = `i' + 1 } >> replace firstdate[`i'] = VisitDate[`i'] if _n==`i' >> } >> * * 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: While/if for individual observations***From:*"Williams, Barbara" <Barbara.Williams@vmmc.org>

**Re: st: While/if for individual observations***From:*Nick Cox <njcoxstata@gmail.com>

**RE: st: While/if for individual observations***From:*"Williams, Barbara" <Barbara.Williams@vmmc.org>

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