I create a preliminary attempt, but I don't match your results for your simulation data. Still, this might help you get started in the right direction. I have to run to a meeting, so I didn't have time to comment the code.
HTH
proc iml;
start PercentRankInList(x, target); /* pct rank when target value is in list */
NLower = ncol(loc(x<target));
NUpper = ncol(loc(x>target));
return( NLower/(NLower+NUpper));
return( pr );
finish;
start PercentRank(x, target); /* pct rank whether or not target value is in list */
idx = loc(x=target);
if ncol(idx)>0 then /* target value is in list */
return(PercentRankInList(x, target));
idxLower = loc(x<target);
idxUpper = loc(x>target);
x0 = max(x[idxLower]);
pr0 = PercentRankInList(x, x0); /* x0 is in list */
x1 = min(x[idxUpper]);
pr1 = PercentRankInList(x, x1); /* x1 is in list */
f = (target-x0)/(x1-x0); /* target is fraction f between x0 and x1 */
return( pr0 + f*(pr1-pr0) ); /* interpolate */
finish;
/* test on examples at
http://office.microsoft.com/en-us/excel-help/percentrank-HP005209212.aspx
*/
/*
x = {13,12,11,8,4,3,2,1,1,1};
print (PercentRank(x, 2));
print (PercentRank(x, 4));
print (PercentRank(x, 8));
print (PercentRank(x, 5));
*/
/* test on simulation example data */
use PercentRank; read all var {b0 b1}; close PercentRank;
print (PercentRank(b0, -17.871));
print (PercentRank(b1, 0.38566));
