Just a little more salt...
Once you begin using a variable you become familiar with its magnitudes...
NNT of 1000 / 5 years for drug treatment is not good!
NNT of 6/1 year is pretty good.
NNT of 100-500 / 5 years seems acceptable for some preventive measures.
If we keep using one currency we will get familiar with it improving
communication. Isn't it what this is all about?
Caveat: in the spririt of Dr Simon, I take care of patients and not numbers
and maybe the above numbers make no sense!
Victor
> ----------
> From: Simon, Steve, PhD[SMTP:[log in to unmask]]
> Reply To: Simon, Steve, PhD
> Sent: Thursday, May 27, 1999 1:07 PM
> To: [log in to unmask]
> Subject: RE: NNTs versus ARRs
>
> Just a couple more comments. This may be boring to some people, but I have
> strong opinions about this issue. We are all awash in a sea of numbers
> (I've
> contributed a few drops to this sea, myself). The trick is to present all
> these numbers in a way that doesn't drown our readers.
>
> Point #1. Rory O'Conor talks about rounding. A good reference for rounding
> is Ehrenberg, A.S.C. (1981) "The Problem of Numeracy," The American
> Statistician, 35(2), 67-71.
>
> Ehrenberg stresses that you should never display three significant
> figures.
> Always display only one or two figures. There are several reasons for
> this.
> One that I remember is that quite often we want to compare two numbers by
> subtracting one from another. It's a whole lot easier to do the
> subtraction
> with numbers like 550 and 480, than with numbers like 549 and 482. Our
> short
> term memory can only hold 3-4 pieces of information, and trying to
> manipulate a pair of three digit numbers will overload short term memory.
>
> In the context of NNTs, you might want to do division instead of
> subtraction, but the same principle applies.
>
> It is difficult emotionally to round to two significant digits, and I find
> myself wanting to include that third digit (as I did in an earlier
> e-mail).
> But that third digit is rarely helpful and it can hinder comprehension.
>
> Point #2. Robert Newcombe argues that with the proper adjustment, small
> fractions are easily assimilable. So even though .00235 is hard to work
> with, 2.35 per thousand is easy to work with. I may be nitpicking, but I
> still disagree. I always prefer working with whole numbers and the NNT is
> usually a nice whole number. Also, I am indecisive by nature, and I hate
> to
> choose between reporting 2.35 per thousand or 235 per hundred thousand.
>
> Point #3. The idea of inverting an absolute risk reduction seems
> unnatural,
> but there is a lot of precedent for such manipulation. We normally think
> nothing of using logarithmic scales for measuring noise and earthquake
> intensity, and the log transformation is a lot more difficult to explain
> than an inverse transformation.
>
> We also use an inverse transformation in other areas. When measuring how
> long it takes for someone to perform a task, we can talk either about time
> (the task takes five minutes) or speed (you complete 12 items every hour).
> I
> switched units on you, but the second number is the inverse of the first
> (and vice versa).
>
> Perhaps this confusion about a confidence interval for NNT containing
> infinity would be less problematic when we remind ourselves that someone
> working at a speed of zero will take an infinite amount of time to
> complete
> the task.
>
> Point #4. When you are trying to decide between an absolute risk reduction
> and a number needed to treat, why not present it both ways? It doesn't add
> that much to the length of a paper, and most of us don't have a calculator
> handy when we are reading JAMA.
>
> Disclaimer#1. Effective presentation of research data is an art more than
> a
> science, and I'm a lousy artist. So take everything I say with a grain of
> salt.
>
> Disclaimer #2. I think the issue of what patients comprehend is an
> important
> one, but this is one area I can't comment on intelligently as I don't see
> patients as part of my job. I'm not qualified to provide health care, but
> my
> Ph.D. in Statistics does allow me to doctor numbers.
>
> Final disclaimer. I don't disagree in substance with what most of the
> others
> have written on this subject. If I do disagree, it is a question of
> degree.
> It's a "yes, but" rather than a "no".
>
> Steve Simon, [log in to unmask], Standard Disclaimer.
> STATS - Steve's Attempt to Teach Statistics: http://www.cmh.edu/stats
>
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
|