options ls=72 ps=55;
data prob2;
input errors group $;
datalines;
19.9 a
15.7 a
9.5 a
9.4 a
8.7 a
8.2 a
7.7 a
7.4 a
7.4 a
7.1 a
6.9 a
6.8 a
6.3 a
5.0 a
4.2 a
4.1 a
2.2 a
14.6 b
8.8 b 
5.4 b
5.1 b
5.0 b
4.3 b
3.9 b
3.3 b
2.4 b
1.7 b
proc sort;
 by group;
proc univariate normal plot;
 var errors;
 by group;
proc npar1way wilcoxon;
 var errors; 
 class group;
run;