Hi Eric
I'm not sure I understand this - would you not have access to the study's
population prevalence (ie you need to know both the number of events and the
number without events to calculate the odds) when calculating the OR? Or are
you referring to knowledge of prevalence in the total population, not just
the study population? If this former should be the case, then should not
most studies be using ORs?
regards
Andrew
> -----Original Message-----
> From: Eric Harvey [SMTP:[log in to unmask]]
> Sent: Thursday, 25 February 1999 09:29
> To: [log in to unmask]
> Subject: Re: Odds Ratios vs Relative Risk
>
> As I understand it, RR can only be used when the population prevalence of
> the measured outcome is known. In many cases, population prevalence is
> not
> known, so OR can be properly used to approximate RR when quantifying rare
> events. As events become more common, OR no longer accurately approximate
> RR. In these cases, OR will overestimate the benefits and harms of
> treatment (RR).
>
> See:
> Sackett DL. Down with odds ratios! Evidence-Based Medicine. 1996
> Sept/Oct;1:(got from ACP website so I don't have page numbers).
>
> -----Original Message-----
> From: Andrew Jull <[log in to unmask]>
> To: [log in to unmask]
> <[log in to unmask]>
> Date: Wednesday, February 24, 1999 11:41 AM
> Subject: Odds Ratios vs Relative Risk
>
>
> >Dear All
> >
> >I was recently conversing with a colleague and the question of why use
> ORs
> >instead RRs came up. My naive response was that the choice seemed to be
> >based on the individual's preference and that I had not read anything
> that
> >suggested the use of one was more informative than another (and indeed
> have
> >read some material that suggests ORs are misleading when the OR is high -
> >but I don't want to get onto that issue).
> >
> >Can anyone help me with why odds ratios might be used in preference to
> >relative risk or vice versa.
> >
> >regards
> >Andrew Jull
> >Clinical Nurse Consultant
> >Auckland Hospital
> >NEW ZEALAND
> >
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
|