The fitted models by various variables (X) were evaluated
based on both r2 (=1 sum squares of residual/corrected total
sum square) and the standard error of estimation
(SEE ¼ ffiPffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi n
i¼1ðYi ^YiÞ
2
q =ðn pÞ