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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

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