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From |
"Salah Mahmud" <salah.mahmud@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Duration and average frequency of examination |

Date |
Tue, 10 Jun 2008 16:51:36 -0500 |

Hi May, I do not have Stata to test the following solution it may need some tweaking: sort id age by id: gen total_duration =age[_N] - age[1] by id: gen average_freq=total_duration /_N hope this helps, salah mahmud On Tue, Jun 10, 2008 at 12:45 PM, MAY BAYDOUN <mbaydoun2002@yahoo.com> wrote: > Dear statalisters, > > I was wondering if you could help me figure out a way > to obtain the frequency at which each individual was > examined (i.e. average number of follow-up visits per > year) and the total duration (i.e. time between first > and last visit) if the dataset is person-period format > and I have the following structure: > > id visit age at visit > 1 1 30 > 1 2 32 > 1 3 36 > 1 4 50 > 2 1 45 > 2 2 46 > 3 3 50 > 3 4 56 > 3 5 60 > 3 6 65 > 4 1 42 > 4 2 48 > > In other words, the distance in age between visits > varies for each individual, the number of visits is > not the same and the age at baseline varies as well. > > So, I would like to obtain the following variables > (made up numbers for frequencies): > > id Freq Duration > 1 0.5 20 > 2 0.4 1 > 3 0.3 15 > 4 0.6 6 > > The duration for individual 1 for example is: > 50-30 > > The average frequency is the tricky one I guess, it is > for individual 1: > [1/(32-30) + 1/(36-32) + 1/(50-36)]/4 > > Thanks a lot and hope to hear from you soon, > > Sincerely yours, > > May > > > May Baydoun, PhD in Epidemiology (UNC-Chapel Hill) > Staff Scientist, > National Institute on Aging, NIH/IRP, Biomedical > Research Center, > Baltimore, MD > > > > > May Baydoun, PhD in Epidemiology (UNC-Chapel Hill) Staff Scientist, National Institute on Aging, NIH/IRP, Biomedical Research Center, Baltimore, MD > > > > * > * For searches and help try: > * http://www.stata.com/support/faqs/res/findit.html > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: Duration and average frequency of examination***From:*MAY BAYDOUN <mbaydoun2002@yahoo.com>

**References**:**st: Duration and average frequency of examination***From:*MAY BAYDOUN <mbaydoun2002@yahoo.com>

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