I'm confused about which predictor gets the "-1" or the "1" when using contrast codes and not dummy codes for recoding variables. For example, I prepared the following contrast codes by following my textbook but I don't understand why I'm doing it this way:
Y variable: time spent at job X variable: type of assessment method: (1) interview, I (2) competency, C (3) written, W
Q. The researcher wants to know if written (W) result in different time spent at a job from applicants assessed with interviews (I) or competency (C). She also wants to determine if there is a difference in time spent at job between interview (I) and competency (C).
My answer (based on textbook):
- New variable 1: I --> +1, C --> +1, W --> -2
- New variable 2: I --> +1, C --> -1, W --> 0
(Because I am comparing comparing the written to interviews or competency and I am also comparing interviews and competency. In addition, this would make my new variables orthogonal since they all add up to 0). Is this the proper way to think about this?
