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08-05-2009 11:43 AM

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

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

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08-06-2009 04:46 AM

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

May it have an influence on the calculation of the ICC ?

Thanks a lot,

Céline

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08-07-2009 12:59 PM

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.

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.

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08-20-2009 05:02 AM

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,

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,

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08-21-2009 09:06 PM

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

All the best to you.

All the best to you.