I am testing a model which involves three variables. I am testing a partial mediation model. In SPSS, when I calculate bivariate correlation among these three variables, the maximum correlation (say between B&C) I get is -.530 . However, using AMOS and testing for discriminant validity, I get the correlation as -.814. This is very high and is creating problems for discriminant validity. Other two correlations between A & B and between C & A remains more or less the same (-.314 and .359 vs -.369 and .429) I am not able to understand why it is happening and what I should be doing to control it.