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gen long obsno = _n expand 2 bysort obsno : gen Time = cond(_n == 1, DateandTimeIN, DateandTimeOUT) by obsno : gen Change = cond(_n == 1, 1, -1) if !missing(Time) sort Time gen sumChange = sum(Change) On Sat, Nov 3, 2012 at 7:51 PM, Scott Simpson <simpsons@uw.edu> wrote: > I have a data set that lists patients' clinic visits. Given each inidividual's time into the clinica and time out of the clinic, I am trying to create a variable that tells me how many patients are in the clinic at a given time. In essence, the clinic population at a given point in time, really, the clinic population at the point the patient arrives. > > I thought I had it by counting the # of pts who had arrived before, then substracting those who left before-- > > sort DateandTimeIN; > gen inorder = _n; > gen inbefore = inorder - 1; > sort DateandTimeOUT; > gen outorder = _n if !missing(DateandTimeOUT); > gen leftbefore = outorder - 1; > sort DateandTimeIN; > gen currentpop = inbefore + 1 - leftbefore; > (Admittedly, there are some unaccounted patients already in clinic before my data starts, will have to manually figure that out and correct.) The output of the above, however, gives me a lot of negative numbers for currentpop, which does not make intuitive sense to me unless the recorded time is incorrect. > > This seems as though would be a common programming question but am not finding answers among local experts or online. Must be a .do file out there for 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/

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