[R] intra-class correlation? coherence among multiple ordinal responses

Daniel Malter daniel at umd.edu
Sat Aug 22 22:39:10 CEST 2009

Thank you, William.


William Revelle wrote:
> At 6:15 PM -0400 8/21/09, Daniel Malter wrote:
>>I have a quick statistical question and hoped somebody has a tip for me
>>without me having to go to the local statistician on Monday.
>>I assess 4 statements from 90 subjects. Each of the 4 statements receives
>>one of three responses (say -1, 0, or 1). I can use Cramer's V or Spearman
>>correlations to assess the correlation between each pair of statements,
>>I am looking for a measure of coherence across/among all 4 statements. To
>>me, this seems to be intraclass correlation. So I was wondering whether I
>>can apply it here (specifically, ICC(2,1) or ICC(3,1)) or whether I should
>>use an alternative procedure given that my responses are ordinal.
> Daniel,
> The intraclass correlation is used if raters are all of the same 
> ``class".  That is, there is no logical way of distinguishing them. 
> Examples include correlations between  pairs of twins, correlations 
> between raters.  If the variables are logically distinguishable 
> (e.g., different items on a test), then the more typical coefficient 
> is based upon the inter-class correlation (e.g., a Pearson r) and a 
> statistic such as alpha or omega might be used.
> The differences between the 3 types of ICCs are the type of 
> generalization you want to make.
> Note that ICC3n is the same as coefficient alpha.
> ICC, alpha, and omega are all part of the psych package.
> Bill
> -- 
> William Revelle		http://personality-project.org/revelle.html
> Professor			http://personality-project.org/personality.html
> Department of Psychology            
> http://www.wcas.northwestern.edu/psych/
> Northwestern University	http://www.northwestern.edu/
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