# Discussion: Should or should not P(Lying | Human) be above or equal to 0,5?

Condition: An human called X, in this specific case, according to game theory will win the most money and lose the least if applying a lying strategy about event Y happening. If he tells the truth about event Y not happening he will lose all the money and go to jail.

If I'm making a decision based on X:s testimony about Y, should I or should I not put P(Lying | Human X gives testimony) to be above or equal to 0,5 and ignore his statement to protect my epistemic vulnerability?

If I put P<0,5 I'm risking making a bad decision because of gullibility and trusting someone who has incentives to lie?

What would I be justified in doing according to you? Should I ignore what game theory tells me?

Many thanks,

• My initial thoughts are simply that since I can't risk being Gullible I therefor can't put P <0.5. Commented Dec 12, 2020 at 0:14
• It seems reasonable to assume that the more agents have to lose or win in a situation, the more of them will chose a winning decision. However any fixed value (like 0.5) does not seem useful with a complex setup, so the whole question seems to lack justification or context for using such a number. 0.5 only seems useful as probability for 2 choices with equal outcomes. I don't think game theory provides you with any number for the case you describe. Commented Dec 13, 2020 at 10:55
• Thanks tkruse. Would you find p > 0.5 in this scenario given only these facts? And if not, why? Commented Dec 13, 2020 at 11:37
• The given facts are not enough to come up with a useful number. Though it looks like you were trying to set up a situation where the real probability of lying is quite high, like 0.9. If that was your intention when providing this example, no rational theory would try to model the situation using a lower number like 0.5. Commented Dec 13, 2020 at 23:16
• Thanks! Would you say that putting p <0.5 makes one take unecessary risk of being gullible and easily fooled? Commented Dec 14, 2020 at 0:19