Credibility and bias. Hello. In Devil's Advocate, Barbara, a high school girl, testifies in court: Defense: Have you ever had a party at your house, Barbara, when your parents were away? Prosecution: Objection. Your Honor, this is way out of line. Defense: Credibility and bias. Judge: Overruled. Answer the question. Barbara: Yes. Any chance you could explain to me what "Credibility and bias" means? It's just not clear to me who's (not?) credible or biased here. Thank you.