## How to compare the difference between each two groups?

Frequent Contributor
Posts: 88

# How to compare the difference between each two groups?

Dear SAS users,

I have the following data set created by a data procedure, what analysis method should I use so that I can know whether there is significant difference between each 2 groups regard to the performance (3 lelvels as Good, Mediate and Bad)?

Since the data is frequency data at each performance level in each group, thus I have no idea.

data result;

input performance \$ group \$ frequency@@;

datalines;

Good Gp1 10 Mediate Gp1 15 Bad Gp1 6

Good Gp2 12 Mediate Gp2 13 Bad Gp2 6

Good Gp3 10 Mediate Gp3 10 Bad Gp3 11

;

run;

Frank Green

Super User
Posts: 10,784

## Re: How to compare the difference between each two groups?

Corresponding Analysis ?

Ksharp

Posts: 3,055

## Re: How to compare the difference between each two groups?

Seems like a chi-squared test in PROC FREQ will answer the question.

--
Paige Miller
Frequent Contributor
Posts: 88

## Re: How to compare the difference between each two groups?

I am afraid, I can't agree with you. If you think freq procedure works, please let me check your code. Per  my understanding, we can't use Freq to do this.

Super User
Posts: 10,784

## Re: How to compare the difference between each two groups?

That would not. chi-squared test is used to check relations between column and row variables.

SAS Employee
Posts: 23

## Re: How to compare the difference between each two groups?

Hi!

I am not a statistician, so I should probably stay out of this thread... Read this with a pinch of salt...

If we have the null hypothesis than there is no difference in the distribution of performance between groups, the code below will give us a p-value of 0.49. So, there is no significant difference between groups.

proc freq data=result;

table group*performance / chisq;

weight frequency;

run;

Super User
Posts: 10,784

## Re: How to compare the difference between each two groups?

"the code below will give us a p-value of 0.49. So, there is no significant difference between groups."

That maybe should said there is no significant relative between groups and performance .

Dr. may give us the exact answer .

Ksharp

Frequent Contributor
Posts: 84

## Re: How to compare the difference between each two groups?

Also you can do (and test with exact trend if you have combine performance into two level):

ods graphics on;

proc freq data=result;

weight frequency;

tables performance*group / chisq cmh measures cl

plots=freqplot(twoway=stacked);

test smdrc;

run;

ods graphics off;

Posts: 2,655

## Re: How to compare the difference between each two groups?

The follow-up pairwise comparisons are the only tricky issue.  Note that the overall test is not significant, so the p values for pair-wise comparisons are bound to be liberal.  My thought is to use exact frequency methods, so I don't understand the objection to PROC FREQ, unless there are other factors involved.

First, the overall test:

proc freq data=result;

weight frequency;

tables performance*group /all;

exact fishers agree;

run;

Then the pair-wise comparisons:

proc freq data=result;

where group in ('Gp1',' Gp2');

weight frequency;

tables performance*group /all;

exact fishers agree;

run;

proc freq data=result;

where group in ('Gp1',' Gp3');

weight frequency;

tables performance*group /all;

exact fishers agree;

run;

proc freq data=result;

where group in ('Gp2',' Gp3');

weight frequency;

tables performance*group /all;

exact fishers agree;

run;

However, there is nothing significant in any of the tests here.

Steve Denham

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