Statalist


[Date Prev][Date Next][Thread Prev][Thread Next][Date index][Thread index]

st: frequency of examination and duration


From   MAY BAYDOUN <mbaydoun2002@yahoo.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: frequency of examination and duration
Date   Tue, 10 Jun 2008 10:07:19 -0700 (PDT)

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


      
*
*   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/



© Copyright 1996–2014 StataCorp LP   |   Terms of use   |   Privacy   |   Contact us   |   What's new   |   Site index