Sender demeanor is an individual difference in the believability of message senders that is conceptually independent of actual honesty. Recent research suggests that sender demeanor may be the most influential source of variation in deception detection judgments. Sender demeanor was varied in five experiments (N = 30, 113, 182, 30, and 35) to create demeanor-veracity matched and demeanor-veracity mismatched conditions. The sender demeanor induction explained as much as 98% of the variance in detection accuracy. Three additional studies (N = 30, 113, and 104) investigated the behavioral profiles of more and less believable senders. The results document the strong impact of sender effects in deception detection and provide an explanation of the low-accuracy ceiling in the previous findings.

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The concept of diagnostic utility was used to create questions that would differentially affect deception detection accuracy. Six deception detection studies show that subtle differences in questioning produced accuracy rates that were predictably, substantially, and reliably above and below chance. The first 3 detection studies demonstrate that diagnostically useful questioning can reliably achieve accuracy rates over 70% with student and experienced judges. The fourth and fifth experiments demonstrated negative diagnostic utility among federal investigators but not students. The final experiment crossed 3 sets of interview questions with experience. Strong question effects produced a swing in accuracy from 32 to 73%. A questioning by experience interaction was also obtained.

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Consistent with the Park and Levine's (PL) probability model of deception detection accuracy, previous research has shown that as the proportion of honest messages increases, there is a corresponding linear increase in correct truth–lie discrimination. Three experiments (N = 120, 205, and 243, respectively) varied the truth–lie base rate in an interactive deception detection task. Linear base‐rate effects were observed in all 3 experiments (average effect r#x02009;= .61) regardless of whether the judges were interactive participants or passive observers, previously acquainted or strangers, or previously exposed to truths or lies. The predictive power of the PL probability model appears robust and extends to interactive deception despite PL's logical incompatibility with interpersonal deception theory.