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st: RE: parametric or non-parametric

From   "Newson, Roger B" <>
To   <>
Subject   st: RE: parametric or non-parametric
Date   Fri, 24 Aug 2007 18:26:57 +0100

I personally would argue that there are no such things as "nonparametric
methods". They should be called "rank methods", and are based on rank
order parameters, which can be estimated with confidence limits. They
are particularly suitable for use with Likert scales (I think). For
details of how to use these methods in Stata, see Newson (2002), Newson
(2006a) and Newson (2008b).

I hope this helps.



Newson R. Parameters behind "nonparametric" statistics: Kendall's tau,
Somers' D and median differences. The Stata Journal 2002; 2(1): 45-64.
Download pre-publication draft from

Newson R. Confidence intervals for rank statistics: Somers' D and
extensions. The Stata Journal 2006a; 6(3): 309-334. Download
pre-publication draft from

Newson R. Confidence intervals for rank statistics: Percentile slopes,
differences, and ratios. The Stata Journal 2006b; 6(4): 497-520.
Download pre-publication draft from

Roger Newson
Lecturer in Medical Statistics
Respiratory Epidemiology and Public Health Group
National Heart and Lung Institute
Imperial College London
Royal Brompton campus
Room 33, Emmanuel Kaye Building
1B Manresa Road
London SW3 6LR
Tel: +44 (0)20 7352 8121 ext 3381
Fax: +44 (0)20 7351 8322
Web page:
Departmental Web page:

Opinions expressed are those of the author, not of the institution.

-----Original Message-----
[] On Behalf Of Jen McCormick
Sent: 24 August 2007 17:38
Subject: st: parametric or non-parametric

I have a question regarding using parametric versus non-parametric 

A colleague and I conducted a national survey (n=845).  Much of our data

are from Likert-scale based questions.  We have been exploring the 
options for analysis and have found some differences of opinion in the 
literature on whether parametric methods should be used with these kind 
of data (versus nonparametric).  My question is whether anyone has had 
experience analyzing Likert scale data (5 point, anchored scale) using 
parametric methods and how you transformed the data to correct for 
non-normal distribution.

Thanks in advance for any suggestions or references.

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