Which one of the following is not correct?

1. Intermediate principal stress is ignored when applying the maximum principal stress theory.
2. The maximum shear stress theory gives the most accurate results amongst all the failure theories.
3. As per the maximum strain energy theory, failure occurs when the strain energy per unit volume exceeds a critical value.
4. As per the maximum distortion energy theory, failure occurs when the distortion energy per unit volume exceeds a critical value.