I suppose it would be because i do not understand the information they are looking for and would not validate any information that was left up to interpretation. I also come to this conclusion based on how often i see psychologist in disagreement with each other. It's my opinion that a lot is left to interpretation of events.
If i pour gas on fire, 100 times out of 100, the same result will happen. I dont feel psychology works with the same precision. Also, how can you measure the ability to fake? seems like that would be a variable in every equation. I can fake every emotion. How does psychology overcome that obstacle with any level of certainty?