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Re: st: Nominal or ordinal?


From   Ronan Conroy <rconroy@rcsi.ie>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: st: Nominal or ordinal?
Date   Fri, 13 Aug 2010 13:42:35 +0100

On 12 Lún 2010, at 21:29, David Bell wrote:

Most of the world is willing to treat scales like this as interval data. Sure it isn't "exactly" interval. Be sure to consider whether your audience will be familiar with interpretations of ordinal logit regressions.

I cannot endorse the behaviour of most of the world, which is usually characterised more by wishful thinking than by reflection.

The assumption of normally distributed error is broken for short ordinal scales, and I refuse to believe that Extremely Likely (4) is twice as much belief as Slightly Likely (2). While a scale made up of many such items will probably exhibit interval properties, this does not apply to the items themselves.

And if your audience doesn't know how to interpret ordinal logistic regression they probably are bluffing about knowing how to interpret OLS regression. In either case, you will have to work hard to explain what you have done. Good luck.


Ronan Conroy
=================================

rconroy@rcsi.ie
Royal College of Surgeons in Ireland
Epidemiology Department,
Beaux Lane House, Dublin 2, Ireland
+353 (0)1 402 2431
+353 (0)87 799 97 95
+353 (0)1 402 2764 (Fax - remember them?)
http://rcsi.academia.edu/RonanConroy

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