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11-04-2012 11:52 AM

Hi,

I have skewed data on which I want to perform multiple comparisons.

I accidentally performed parametric test which had the following code:

proc glm data=work PLOTS=(DIAGNOSTICS RESIDUALS);

class type;

model results=type;

estimate " " type 3 -1 -1 -1/e;

estimate " " type -1 3 -1 -1/e;

estimate " " type -1 -1 3 -1/e;

estimate " " type -1 -1 -1 3/e;

estimate " " type 2 0 -1 -1/e;

estimate " " type 0 0 -1 1/e;

estimate " " type -1 1 0 0/e;

run;

quit;

I now want to make the non-parametric version of that.... I don't know what to do

So far I have:

PROC NPAR1WAY data=work wilcoxon;

Class TYPE;

Var results;

Run;

Which is fine, but then to make multiple comparisons I don't know what to do.

Proc Multtest has been reccomended to me but I don't follow the syntax on the SAS site, and it all seems to give t-test results which seem imappropriate. I am supposed to use the option "HOCHBERG" I believe.

Does anyone know how to help me?

Thanks

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Posted in reply to katiexyz

11-04-2012 02:46 PM

Here is one way of doing all the tests and corrections (assuming variable **type** is numeric with values=1,2,3,4) :

**data tests;****input testId $ type grp;****datalines;****test3111 1 1****test3111 2 2****test3111 3 2****test3111 4 2****test1311 1 2****test1311 2 1****test1311 3 2****test1311 4 2****test1131 1 2****test1131 2 2****test1131 3 1****test1131 4 2****test1113 1 2****test1113 2 2****test1113 3 2****test1113 4 1****test2011 1 2****test2011 3 1****test2011 4 1****test0011 3 1****test0011 4 2****test1100 1 1****test1100 2 2****;**

**proc sql;****create table workGrp as****select T.testId, T.grp, W.results****from work as W inner join tests as T**** on W.type=T.type****order by testId, grp;****quit;**

**proc npar1way data=workGrp wilcoxon;****by testId;****class grp;****var results;****ods output WilcoxonTest=Wtests;****run;**

**proc multtest HOCHBERG out=adjustedWtests**** inpvalues(nValue1)=Wtests(where=(name1="P2_WIL"));****run;**

**proc print data=adjustedWtests; run;**

PG

PG

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Posted in reply to PGStats

11-04-2012 09:42 PM

PG,

There is no need to use proc npar1way since OP want multiple comparisons , not two comparison.

proc glm is also a candidate .

Ksharp

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Posted in reply to PGStats

11-05-2012 03:34 AM

I have no idea what either of you are talking about.

PG Stats: Why would I use proc sql? I don't know what any of that code means.

Ksharp: It isn't a linear model, I have non normal data so how can I use proc glm? Deffo proc par1way.

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Posted in reply to katiexyz

11-05-2012 07:58 AM

Here is another approach. Use PROC MIXED to analyze the ranks, rather than the raw results. Something like:

proc rank data=work out=rankeddata;

var results;

ranks rank_result;

run;

/* Change to PROC MIXED to get LSMESTIMATEs, which can be adjusted for multiple comparisons, and to accommodate the comparisons which are not just one group to another. Multiple comparisons are the stepdown Bonferroni (Holm) adjustment */

proc mixed data=rankeddata ;

class type;

model rank_result=type;

lsmestimate type 'Type 1 vs mean of remaining' 3 -1 -1 -1,

lsmestimate type 'Type 2 vs mean of remaining' -1 3 -1 -1,

lsmestimate type 'Type 3 vs mean of remaining' -1 -1 3 -1,

lsmestimate type 'Type 4 vs mean of remaining' -1 -1 -1 3,

lsmestimate type 'Type 1 vs mean of types 3 and 4' 2 0 -1 -1,

lsmestimate type 'Type 3 vs type 4' 0 0 -1 1,

lsmestimate type 'Type 1 vs type 2' -1 1 0 0/adjust=bon stepdown;

ods output lsmestimates=lsmestimates;

run;

/* If you want the Hochberg adjustment, then add the following. See Example 61.5 Inputting Raw p-Values in the MULTTEST Procedure documentation. In particular, read the last paragraph in this example, describing some general assumptions regarding the methods of adjustment */

/* First, pare down the lsmestimates dataset to just the labels and the p values */

data lsmestimates_for_multtest;

set lsmestimates;

raw_p=probt;

keep label raw_p;

run;

/*Now run the adjustments. This will give adjustments using the stepdown Bonferroni (Holm, same as in PROC MIXED, hopefully), Hochberg and false discovery rate methods*/

proc multtest inpvalues=lsmestimates_for_multtest holm hoc fdr;

run;

Good luck.

Steve Denham

Message was edited by: Steve Denham

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Posted in reply to katiexyz

11-05-2012 10:06 AM

In my code above, many versions of your data are created, one for each of your estimate statements. In each version, the data is divided in two groups. Then npar1way is called to do all the Wilcoxon tests and multtest is called to correct the p-values for multiple testing.

PG

PG