Stata The Stata listserver
[Date Prev][Date Next][Thread Prev][Thread Next][Date index][Thread index]

st: Attributable fraction


From   "Andrea Baccarelli" <andreastata5@hotmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Attributable fraction
Date   Tue, 16 Dec 2003 20:22:52 +0000

I tried the command "aflogit" to obtain adjusted Population Attributable Fractions (PAFs) after logistic regression (command "logistic").

I have 3 questions:

1. The command seemed not to work properly. I carefully followed the instruction but I received the error message "l_1 not found". I was wondering whether the command still works on Stata 8.0
Anyway, the error message appeared after the PAF for the variable I was interested in had been displayed. Also, the command worked fine when no dummy variables were used (i.e., the "xi" function was not used)

2. If I am correct, the command simply:
a. gets the OR from the estimation produced by "logistic" (in my case OR=3.7)
b. then calculates the AF in the exposed subjects (EAF), i.e., (3.7-1)/3.7=0.73
c. Multiplies the EAF for the prevalence of the exposure among cases (0.29 in my case). i.e., 0.73*0.29=0.21
Is that correct?

3. The help file says that the command calculates (function "cc") PAFs from data that come from an unmatched case-control study. Why "Unmatched"? Does that simply mean that the command do not work with "clogit" as I understant from the help (therefore, matched refers to 1:1 matching?)?
My case-control study has a frequency matching. Is it not correct to use the command (and the formula above at point 2) when a matching is present?

Thanks a lot,

Andrea

Andrea Baccarelli, MD, MPH, PhD
Genetic Epidemiology Branch
Division of Cancer Epidemiology and Genetics
National Cancer Institute, NIH, DHHS
6120 Executive Blvd. - EPS 7110
Bethesda, MD 20892-7236
Tel. (301)-496-5786
Fax (301)-402-4489
baccarea@mail.nih.gov

_________________________________________________________________
Enjoy the holiday season with great tips from MSN. http://special.msn.com/network/happyholidays.armx

*
* 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