# st: R: What does -koopmani- output? odds ratios or risk ratios?

 From Carlo Lazzaro To statalist@hsphsun2.harvard.edu Subject st: R: What does -koopmani- output? odds ratios or risk ratios? Date Fri, 13 Mar 2009 19:14:23 +0100

```Dear Tiago,
I actually do not know the features of -koopmani-. However, sticking to
basic epidemiological formulae, I would agree with you. In fact, apart from
95% CI, the point estimate of OR should be 36, whereas the point estimate of
RR (as you state), turns out to be 4.5. However, as reported in the
following article (please, find the reference below), there's sometimes some
"straddling" between OR and RR. Hence, it may be that, in your example, the
OR is in fact the ratio (.9/.2=4.5) between the estimate of the probability
of having the event in Group 1 (ie 36/40=.9) and in Group 2 (ie 16/80=.2),
respectively

Jun Zhang; Kai F. Yu
Odds Ratio in Cohort Studies of Common Outcomes
What's the Relative Risk?: A Method of Correcting the
http://jama.ama-assn.org/cgi/content/full/280/19/1690

Sorry I cannot give you a more helpful hint.

Kind Regards and enjoy your W_E,
Carlo

-----Messaggio originale-----
Da: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] Per conto di Tiago V. Pereira
Inviato: venerdì 13 marzo 2009 16.57
A: statalist@hsphsun2.harvard.edu
Oggetto: st: What does -koopmani- output? odds ratios or risk ratios?

Dear statalisters,

Working with -koopmani-, one types:

.  koopmani 36 40 16 80

and gets:

|            Event       |            Proportion
|       Yes          No  |     Total         Yes
-----------------+------------------------+----------------------
Group1 |        36           4  |        40      0.9000
Group2 |        16          64  |        80      0.2000
-----------------+------------------------+----------------------
Total |        52          68  |       120      0.4333
|                        |
|      Point estimate    |  [95% Conf. Interval]
-----------------|------------------------+----------------------
Odds Ratio |              4.5       |  2.939633    7.152252
-----------------------------------------------------------------

That estimate of 4.5 is actually the risk ratio, isn´t it? Or am I doing a
big confusion?

. cci 36 4 16 64

All the best,

Tiago

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```