Because the times are likely to be heavily skewed (to the left) the
difference between mean and median may be considerable.
e.g.
In a previously left skewed distribution, the addition of a new late
thrombolysis decision to the data will do the following:-
The mean will be affected by both the number, and the magnitude of the
difference from the original mean (i.e. slightly over time will move the
mean only a little - well over time will move it more)
The median will at worst move one to the right (the next time a thrombolysis
decision was made in that data set) regardless if it was at 3 hours or 3
weeks!
Medians are very much to our advantage as in a left skew distribution they
will always be less than the mean!!
Simon
Too much maths on the list recently?
Simon Carley
SpR in Emergency Medicine
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Evidence based emergency medicine
http://www.bestbets.org
----- Original Message -----
From: "Jel Coward" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, April 15, 2002 7:09 AM
Subject: Re: Coronary Heart Disease Collaborative (England)
> In article <000b01c1e385$905db3a0$0d210a0a@ntw852>, Katherine Henderson
> <[log in to unmask]> writes
> > The target is a % of the patients- 75% in under 30 minutes now and
> > under 20 minutes by March 2003. However whenever any other numbers
> > are quoted it should be in the form of a median - it does not
> > really make sense to use a mean to look at the performance of a
> > system, and seems to be well accepted by the DOH that median is the
> > right stat.
> >
> I, like Simon, am a bit confused here. My stats base is not great so
> could someone explain to me please why the median is the right statistic
> for looking at the performance of a system rather than me just having to
> trust that it must be so because the govt says so?
>
> Cheers
> --
> Jel Coward
>
> The UK Wilderness Emergency Medical Technician and Command Physician
course is
> 10-16th November 2002 at Glenmore Lodge, Aviemore, Scotland
>
> http://www.wildmedic.org
> http://www.wemsi.org
>
> [log in to unmask]
>
> 'There's no such thing as bad weather - just bad clothing"
> Anon Norwegian
>
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