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From |
"Tiago V. Pereira" <tiago.pereira@mbe.bio.br> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
RE: st: Recovering cell values from odds ratios |

Date |
Tue, 31 May 2011 16:09:54 -0300 (BRT) |

Carina is asking for an approach to reconstruct raw 2x2 tables from the reported odds ratio and its confidence intervals. -- Carina, The solution for your problem is easy, and can be found here: Four-fold table cell frequencies imputation in meta analysis. Carlo Di Pietrantonj, Issue Statistics in Medicine, Volume 25, Issue 13, pages 2299?2322, 15 July 2006 I have used it before, and works really well as long as your summary estimates are reported with some good precision, say, >2 digits (e.g. 1.812). The approach is very simple, and can be done with a hand calculator. You can implement it in Stata as well, and using simple math. Cheers! Tiago *------------------------------------------------------ Thanks for replying, but I think I'm a bit confused, I've attached the example I'm using: Cases: 218 Controls: 14748 Total: 14966 Risk factor: OR: p: case exposed(a): control exposed (b): case unexposed(c): control unexposed(d): Unconsciousness 3.54 0.77973 48 3248 170 11500 Age >65 years 1.69 0.62825 81 5483 137 9265 Female gender 1.66 0.62406 82 5544 136 9204 With the method you describe, the p for each comes out as shown above and consequently the numbers in each group. BUT when I then checked by recalculating the odds ratio from the numbers given, they all equal 1. What am I missing? Thank you! Carina -----Original Message----- From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Maarten Buis Sent: 31 May 2011 12:25 To: statalist@hsphsun2.harvard.edu Subject: Re: st: Recovering cell values from odds ratios On Tue, May 31, 2011 at 1:06 PM, King, Carina <c.king09@imperial.ac.uk> wrote: > I am trying to convert odds ratios back to the raw numbers. I have information on the number of cases and number of controls, as well as the odds ratios and confidence intervals. For that you also need the baseline odds, i.e. the odds of "success" (the expected number of successes per failure) for the controls. The odds for the cases are the odds ratio times the baseline odds. You can transform those odds to probabilities using the formula p = o/(1+o), where p is probability and o = odds. From there you can compute your counts by multiplying the probabilities with the number of controls or cases. Hope this helps, Maarten -------------------------- Maarten L. Buis Institut fuer Soziologie Universitaet Tuebingen Wilhelmstrasse 36 72074 Tuebingen Germany * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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