I think the best option to display what you describe is to use a boxplot grouped by sample. Here is a little program to simulate the idea:
data sample;
do x=1 to 4;
if x < 4 then samp=40;
else samp=100;
do t=1 to 10;
response=ranuni(123);
output;
end;
end;
run;
proc sgplot data=sample;
vbox response / category=x group=samp groupdisplay=overlay connect=mean;
run;
If you don't want the color change, the other option is to do as @ballardw suggested, and that was pre-compute the mean and overlay an annotated line or a SERIES plot.
Hope this helps!
Dan
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