topic Re: Intraclass correlation coefficient (ICC) with macro intracc from SAS in Statistical Procedures

Intraclass correlation coefficient (ICC) with macro intracc from SAS

Celine_France — Wed, 05 Aug 2009 15:43:20 GMT

Good evening,

on the SAS support, I've found the macro intracc which calculates the intraclass correlation coefficient.
In books, it is written that this value is between 0 and 1. However, with some data (where judges give very different marks) and using the macro, I've found negative values.
Is there an error in the macro ? Shall I changed these values to 0 ?

Thanks a lot,

Céline

Re: Intraclass correlation coefficient (ICC) with macro intracc from SAS

Celine_France — Thu, 06 Aug 2009 08:46:25 GMT

I've forgotten to precise that I work on difference of marks, which means that I can have negative values.
May it have an influence on the calculation of the ICC ?

Thanks a lot,

Céline

Re: Intraclass correlation coefficient (ICC) with macro intracc from SAS

statsplank — Fri, 07 Aug 2009 16:59:59 GMT

Hi Celine_France,

No, it doesn't matter if your data values are negative.

In general, there could be situations leading to negative estimates of ICC. It depends on how variance components used to calculate ICC are estimated. I am not familiar with this macro so I can only guess that the method of moments is applied.

Re: Intraclass correlation coefficient (ICC) with macro intracc from SAS

Celine_France — Thu, 20 Aug 2009 09:02:11 GMT

Thanks a lot Statsplank !

I've done some researches about this topic and if ICC is negative, it is because intra-group variance is higher than inter-group variance.

Some documents explain that if ICC is negative, we can conclude to no agreement between the raters. Do you think that I can conclude to that in my case ?

By advance, thanks a lot,

Re: Intraclass correlation coefficient (ICC) with macro intracc from SAS

statsplank — Sat, 22 Aug 2009 01:06:46 GMT

I would think so... Although you should probably discuss it with somebody who has more experience in this area.

All the best to you.