Hi williaml,
Here is my example dataframe
data.frame(
stringsAsFactors = FALSE,
Perspective = c("PBB","CWBB","OFBB","PBB",
"CWBB","OFBB","PBB","CWBB","OFBB","PBB","CWBB",
"OFBB","PBB","CWBB","OFBB","PBB","CWBB","OFBB","PBB",
"CWBB","OFBB","PBB","CWBB","OFBB","PBB","CWBB",
"OFBB","PBB","CWBB","OFBB","PBB","CWBB","OFBB","PBB",
"CWBB","OFBB","PBB","CWBB","OFBB","PBB","CWBB",
"OFBB","PBB","CWBB","OFBB"),
Values = c(5,4,5,5,2,4,5,2,4,3,5,
3,5,2,3,5,3,4,2,3,3,4,2,4,3,3,4,5,3,4,
2,3,3,5,1,5,2,2,3,4,1,4,5,5,5),
Study = c(1,1,1,1,1,1,1,1,1,1,1,
1,1,1,1,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
2,2,2,2,2,2,2,2,2,2,2,2,2,2,2)
)