/****************   Polarity Analysis *****************
Author: William Chambers, PhD
        Experior Assessments
        Gainesville, Florida
        1-800-888-8421  ext 361
Date:   17 Aug 2000

This code is provided gratis, without warrantee.
This code is licensed at no charge to all third parties, 
but proprietary modifications of the code are not allowed.
*********************************************************/

/* this program calculates the polarity score in corresponding correlations */


format /m1 /rd 6,2;

n=100;

/*define variables and causal model*/

 x1=rndu(n,1);
 zx1=((x1-meanc(x1))./stdc(x1));

 x2=rndu(n,1);
 zx2=(x2-meanc(x2))./stdc(x2);

 
y1=(zx1+zx2);
zy1=(y1-meanc(y1))./stdc(y1);




/* The Causal Model */

x=zx1~zx2~zy1;     /* Measured Variables */


/* creates extremes/mid ranges by hypothesized DV (third variable)*/

nr=rows(x);
lo=seqa(1,1,nr./4);
hi=seqa((3.*(nr./4))+1,1,nr./4);
ext=lo|hi;
mid=seqa(((nr./4))+1,1,nr./2);


/****** Sort Here **********/

xby=sortc(x,3); /*sort by third measured variable */

/***************************/

/***** partition into extremes and midranges */
exy=submat(xby,ext,0);  /*extremes of dv */
midy=submat(xby,mid,0); /* midrange of dv */


/* finds correlation between 1st and 2nd variables in the extremes of third*/
cexy= corrx(exy);
/*sexy=(cexy./abs(cexy)).*(cexy.*cexy);*/
      

/*correlations between first two (x1 and x2) in the midrange of third (y) */
cmidy= corrx(midy);
/*semidy=(cmidy./abs(cmidy)).*(cmidy.*cmidy); */
result=cexy~cmidy;

pol1=submat(result(1,3));
pol2=submat(result(1,5));

polar=((pol1.*pol1).*(pol1./abs(pol1))).*((pol2.*pol2).*(pol2./abs(pol2)));
pols=pol1~pol2~polar;
print;



print "Polarity Analysis for Corresponding Correlations ";
print;
print "Correlations between 1st and 2nd variables across ranges of 3rd variable";
print;

    print"          Ext3   Mid3  Polarity";
print ;
print "        " pols;