[R] Negative value for adjustedRandIndex?

[Gavin Simpson]

On Thu, 2009-05-21 at 05:28 -0700, Pooka wrote:
> Hello, 
> 
> I am a very new user to R so please have patience with me. :clap:
> 
> I am trying to evalute the "internal response" for a couple of different
> cluster methods with the help of the AdjustedRandIndex, which is included in
> the mclust package. 
> 
> However, I do get a bit puzzled when I get a negative value as the value
> should be in intervall of [0,1], am I correct?

0 indicates the agreement between your two raters is the same as the
agreement you'd expect to get as a result of random chance. A negative
value therefore indicates that the agreement between the two raters is
even lower than that.

G

>  Have I done something wrong?
> Or should I interpret the negative value as the two methods do not group the
> cases to the same cluster?
> 
> I have for example used k-means and k-median, and choosen five clusters. 
> Each respondent has been labelled as either beloning to cluster 1,2,3,4 or
> 5. I have picked out the first 32 respondents. 
> 
> Example:
> 
> 
> a   <- c(1,2,3,4,5,2,1,5,1,2,2,4,2,3,3,2,4,5,5,4,4,4,5,5,2,3,1,5,5,5,4,1)
> b   <- c(5,5,5,2,5,3,2,2,2,5,3,4,5,5,2,5,2,3,5,5,5,3,5,3,3,2,4,5,2,2,2,3)
> adjustedRandIndex (a,b)
> 
> [1] -0.01608168
> 
> 
> 
> Thanks in advance,
> 
> Pooka
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