Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
st: Question about ir
From
"Reg Jordan" <[email protected]>
To
<[email protected]>
Subject
st: Question about ir
Date
Wed, 7 Nov 2012 10:03:31 -0500
Stata 12.1 updated, Win7 64-bit system
I have a dataset from which I would like to determine the incidence rate of
coronary heart disease (chd) by BMI class.
ir var(cases) var(exposed) risk time, by(bmiclass) , should work, but
I'm having problems with var(exposed). It should be the number of subjects
in each bmiclass, but how do I express this as a variable?
bmiclass | N
---------------+----------
1. underweight | 57
2. normal | 1936
3. overweight | 1845
4. obese | 596
---------------+----------
Total | 4434
--------------------------
I suppose I could use another variable, like sex1:
Summary for variables: sex1
by categories of: bmiclass (BMI index)
bmiclass | N
---------------+----------
1. underweight | 57
2. normal | 1936
3. overweight | 1845
4. obese | 596
---------------+----------
Total | 4434
--------------------------
But
. ir chd sex1 time, by(bmiclass) yields
BMI index | IRR [95% Conf. Interval] M-H Weight
-----------------+-------------------------------------------------
1. underweight | . . . 0
2. normal | . . . 0
3. overweight | . . . 0
4. obese | . . . 0
-----------------+-------------------------------------------------
Crude | . . .
(exact)
M-H combined | . . .
-------------------------------------------------------------------
A brute force approach yields, for example
. ir chd sex1 time if bmiclass == 1
| Sex, exam 1 |
| Exposed Unexposed | Total
-----------------+------------------------+------------
Incident Hosp MI | 6 0 | 6
Time [years] to | 1119.57 0 | 1119.57
-----------------+------------------------+------------
|
|
Incidence rate | .0053592 . | .0053592
|
|
| Point estimate |
[95% Conf. Interval]
|------------------------+------------------------
Inc. rate diff. | . |
. .
Inc. rate ratio | . |
. .
Attr. frac. ex. | 1 |
. 1
Attr. frac. pop | 1 |
+-------------------------------------------------
(midp) Pr(k>=6) = 0.5000 (exact)
(midp) 2*Pr(k>=6) = 1.0000 (exact)
Thanks for your assistance.
Reg Jordan
*
* 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/