Programming the statistical procedures from SAS

Why there is not report of Gamma value to indicate the association

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Why there is not report of Gamma value to indicate the association

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Dear All,

 

I am using PROC FREQ to get the proportion of discordant pairs and its 90% Confidence interval. However, I found one special case when the Binary response all equal to 1, then there is no report on the ODDS ratio, Gamma, etc.

 

Anybody can help me to figure out this? To my understanding, if all binary Response equal to 1, then the Gamma value should be 1.

Many thanks for your help to me on this.

proc freq data=dar_s order=data;  
	tables drgdsc1a* SWAEVL2C/measures CL;
run;

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‎08-11-2016 02:31 AM
SAS Super FREQ
Posts: 3,555

Re: Why there is not report of Gamma value to indicate the association

These measures of association are defined for ordinal variables in two-way tables. From the doc: "A pair is concordant if the observation with the larger value of X also has the larger value of Y."  (X=row variable; Y=column variable)

 

In your example, the Y variable has only one value. There is no "larger value of Y" to use to define pairs as condordant or discordant. Thus any formula that uses "number of condordant pairs" is undefined.

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SAS Super FREQ
Posts: 3,555

Re: Why there is not report of Gamma value to indicate the association

Check the log. Is there a NOTE that says:


NOTE: No statistics are computed for drgdsla *  SWAEVL2C because SWAEVL2C has less than 2 nonmissing levels.

Solution
‎08-11-2016 02:31 AM
SAS Super FREQ
Posts: 3,555

Re: Why there is not report of Gamma value to indicate the association

These measures of association are defined for ordinal variables in two-way tables. From the doc: "A pair is concordant if the observation with the larger value of X also has the larger value of Y."  (X=row variable; Y=column variable)

 

In your example, the Y variable has only one value. There is no "larger value of Y" to use to define pairs as condordant or discordant. Thus any formula that uses "number of condordant pairs" is undefined.

Frequent Contributor
Posts: 87

Re: Why there is not report of Gamma value to indicate the association

[ Edited ]

Dear Rick,

 

You ansswered my question perfectly. I understand the "concordant and discordant" more clearly with you post.

 

Best,

Jack

Super User
Posts: 9,779

Re: Why there is not report of Gamma value to indicate the association


As Rick pointed out, you can't get Gamma due to there is only one level(value 1) of SWAVEL2C.
Gamma measure the correlation between row variable and col variable, so you can't get it if col variable only have one level.

Frequent Contributor
Posts: 87

Re: Why there is not report of Gamma value to indicate the association

Great thanks, got now.

 

☑ This topic is solved.

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