Re: st: Nominal or ordinal?

[Ronan Conroy <rconroy@rcsi.ie>]

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

P    Before printing, think about the environment





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