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

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

Subject |
RE: st: AW: simple sum() question |

Date |
Wed, 15 Apr 2009 17:07:28 +0100 |

Unless there are further complications as yet unrevealed, bysort id : gen visits = _N is a direct and simple solution. If you just wanted to count a subset, then gen interesting = <binary variable defining interesting> bysort interesting id : gen interesting_visits = _N if interesting There are -egen- routes as well, but for problems like this going back to basics is difficult to beat. See also 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 if a tutorial is needed. That's free on-line at the Stata Journal website. Note that even if you did want a collapsed dataset, -contract- rather than -collapse- is more direct. Nick n.j.cox@durham.ac.uk Shehzad Ali Hi Martin and Josiane, Thank you for your replies. You are right that I am interested in the total count of visits for each patient and not the running sum. Sorry, I should have mentioned that patients who had three visits, for instance, have three observations, and those with two visits have two observations. Therefore, the total number of observations for 100 patients is less than 400 (I had made up hypothetical numbers in haste to simplify the case. Not always a good idea). With Martin's solution, I will need to have four observations for each patient (sorry this was my fault as I didn't provide the correct information). With Josiane's suggestion, the dataset collapses which is not what I want. Can you suggest a modified solution please? Again, sorry for the unclear email earlier. On Apr 15 2009, Martin Weiss wrote: > I am betting that you want a count of visits, not a running sum, but > correct me if I am wrong... >clear* >set obs 400 >egen float patient = seq(), from(1) to(400) block(4) >egen float visit = seq(), from(1) to(4) block(1) > >//not strictly necessary >xtset patient visit > >//less than 4 visits for some >replace visit =. if runiform()<0.05 > >bys patient: egen overallvisits=count(visit) > >l in 1/20, sepby(patient) noo >************* Shehzad Ali >I have a simple question about summing across observations. I have 100 >patients (variable: patient_id) in the dataset, each had clinic visits >(variable: clinic) and hospital visits (variable: hospital) recorded at >weeks 4, 8, 12 and 16. The dataset is long and hence I have 400 >observations (one observation per patient per time point). > > I want to sum the clinic visits for each patient (across all 4 visits) > bearing in mind that some patients had less than 4 visits. So effectively > I want to generate a new variable that will produce the sum of clinic > visits for each patient. * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**RE: st: AW: simple sum() question***From:*Shehzad Ali <sia500@york.ac.uk>

**References**:**st: simple sum() question***From:*Shehzad Ali <sia500@york.ac.uk>

**st: AW: simple sum() question***From:*"Martin Weiss" <martin.weiss1@gmx.de>

**Re: st: AW: simple sum() question***From:*Shehzad Ali <sia500@york.ac.uk>

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