topic Re: Why there is not report of Gamma value to indicate the association in Statistical Procedures

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

Jack2012 — Wed, 10 Aug 2016 11:59:48 GMT

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;

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

Rick_SAS — Wed, 10 Aug 2016 12:18:32 GMT

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.

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

Rick_SAS — Wed, 10 Aug 2016 12:35:37 GMT

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.

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

Jack2012 — Thu, 11 Aug 2016 07:40:35 GMT

Dear Rick,

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

Best,

Jack

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

Ksharp — Thu, 11 Aug 2016 06:46:53 GMT


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.

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

Jack2012 — Thu, 11 Aug 2016 07:41:16 GMT

Great thanks, got now.