I want to compare different data in 1 variable (class). For example, i want to compare student in class 6, class 7 and class 8 with another variable, which are student's scores, so i code like this in new data set: If class = 6  then class_6 =1 (class 6 is new variable) Else If class = 7 then class_6=0 and i do similar for class 7 and 8; my proc reg :data=labla; Model score = Class_6 class_7 class_8; Run;  However,  I get this not when use proc reg , i think because there are many class beside 6,7 and 8 in variable class and I just want to compare these three, which lead to this note.: Model is not full rank. Least-squares solutions for the parameters are not unique. Some statistics will be misleading. A reported DF of 0 or B means that the estimate is biased.   what can i do to solve this problem, is there any better way to find out and compare score of class6,7,8 besides proc reg, thank you.  ... View more