The authors of this article declare no conflict of interest.
Truth tellers sound more plausible than lie tellers. Plausibility ratings do not require much time or cognitive resources, but a disadvantage is that it is measured subjectively on Likert scales. The aim of the current paper was to understand if plausibility can be predicted by three other verbal veracity cues that can be measured objectively by counting their frequency of occurrence: details, complications, and verifiable sources. If these objective cues could predict plausibility, observers could be instructed to pay attention to them when judging plausibility, which would make plausibility ratings somewhat more objective. We therefore re-analysed five existing datasets; all of them included plausibility, details and complications and two of them also verifiable sources as dependent variables. Plausibility was positively correlated with all three other tested cues, but mostly predicted by complications and verifiable sources, explaining on average almost 40% of the variance. Plausibility showed larger effect sizes in distinguishing truth tellers from lie tellers than the three other cues, perhaps because the plausibility cue consists of multiple components (complications and verifiable sources). Research has shown that the cues that showed the strongest relationship with veracity typically consisted of multiple components.
Las personas que dicen la verdad suenan más creibles que las mentirosas. La valoración de la credibilidad no necesita mucho tiempo ni recursos cognitivos, aunque tenga la desventaja de que se mide subjetivamente en escalas Likert. El objetivo de este trabajo es saber si la credibilidad puede predecirse mediante pistas de veracidad verbal que puede medirse objetivamente contando la frecuencia de ocurrencia: detalles, complicaciones y fuentes verificables. Si estas pistas cognitivas pudieran predecir la credibilidad se podría instruir a los observadores a que les presten atención al valorar la credibilidad, lo que haría que esta fuera algo más objetiva. Con esta intención reanalizamos cinco conjuntos de datos, todos los cuales incluían credibilidad, detalles y complicaciones y dos de ellos además fuentes verificables como variables dependientes. La credibilidad correlacionaba positivamente con las otras tres pistas que se probaron, predicha sobre todo por las complicaciones y las fuentes verificables, que explicaban de media casi el 40% de la varianza. La credibilidad mostró tamaños de efecto al distinguir personas que decían la verdad de las que mentían mayores que las otras tres pistas, tal vez porque la señal de plausibilidad tiene varios componentes (complicaciones y fuentes verificables). Según la investigación, las pistas con una relación más estrecha con la veracidad normalmente constaban de diversos componentes.
In 2003 Bella DePaulo et colleagues (
Given that plausibility was more strongly related to veracity than most other verbal cues, someone would expect researchers to have included plausibility in the set of verbal cues they examine when assessing veracity. This did not happen. To date at least six frequently cited verbal veracity assessment protocols exist, but in five of them plausibility is not included: Assessment Criteria Indicative of Deception (ACID;
We do not know why other researchers do not include plausibility in their protocols, but for us subjectivity of coding is the main reason to exclude it. Subjectivity means that we cannot explain to practitioners how to use plausibility as a verbal veracity cue. However, ignoring plausibility could be considered a shortcoming, not only because research has shown that plausibility has potential as a veracity assessment cue but also because in our conversations with practitioners about verbal cues to deception they frequently ask us about this cue. Against this background we decided to start examining plausibility in more detail, resulting in the current project which should be seen as a first step. In the current project we explored to what extent plausibility could be predicted by verbal cues that are coded more objectively and that discriminate truth tellers from lie tellers according to research. If plausibility could be predicted by such cues, we would be one step closer to making the concept of statement plausibility more objective. That is, observers could be instructed to consider these objective cues when judging plausibility.
We checked our datasets and found five in which we examined plausibility and two other verbal cues we thought may be related to it: total details and complications (
The objective verbal cues we considered were details, complications, and verifiable sources. Details refer to the meaningful units of information in a statement. Truth tellers typically report more details than lie tellers (
All three cues may be related to statement plausibility. Regarding details, people typically underestimate forgetting (
We re-analysed five datasets (
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When verifiable sources was included as a predictor in the regression, 41% to 60% of the variance was explained. Verifiable sources contributed to explaining the model’s variance, either more than details or more than both details and complications. These results demonstrate that complications and verifiable sources better predict plausibility than details.
Plausibility was positively correlated with details, complications, and verifiable sources but was mostly predicted by complications and verifiable sources. These cues explained 37.29% of the variance (average of the seven
Using total details as a possible predictor for plausibility may be another reason as to why a substantial amount of variance remained unexplained. Total details is a rough measure that gives all details equal weight. In reality some details may be more important to explain plausibility than others. This would resemble the Model Statement findings. A Model Statement is an example of a detailed account unrelated to the topic of investigation (
Statement plausibility was a diagnostic cue to veracity in all five experiments, and it showed larger effect sizes than the other three objectively assessed verbal cues: details, complications, and verifiable sources. A relatively strong performance from plausibility in discriminating between truth tellers and lie tellers was also found in
The strong performance of plausibility in distinguishing truth tellers from lie tellers makes it an attractive verbal cue. In addition, given how difficult and time-consuming it is to count objective cues such as details, complications, and verifiable sources, rating statement plausibility on a Likert scale may save time as well as cognitive resources. This is crucial for investigative practitioners who are frequently under pressure to resolve cases rapidly (
In terms of research, first, we encourage deception researchers to start including plausibility as a cue in their research to further test its diagnostic value but also to examine which objective cues can explain plausibility. The latter results could lead to a more objective way to measure statement plausibility. Second, in the five experiments discussed in this article, plausibility was always defined as “how likely it is that the activities happened in the way described”. Research could examine whether providing observers with different definitions of plausibility would lead to different results. For example, would the definition “how likely it is that the category of activity that is described in this statement generally happens in the way described” lead to different results? Based on the current findings the definition “how likely the overall statement includes complications and verifiable sources given the context” is worth examining.
Third, the five experiments in this paper used samples of college students or community members. It may be useful to examine plausibility among forensic suspects. Suspects and inmates typically do not provide detailed statements and prefer to keep their stories simple, but at the same time, they strive to sound plausible (
Fourth, future research could examine true statements that attract low plausibility ratings and false statements that attract high plausibility ratings. Is there something beyond different types of detail that triggers those incorrect plausibility ratings? For example, are rare events seen as implausible regardless of their veracity? And are statements that are considered to be against someone’s self-interest seen as implausible regardless of their veracity?
We think there is a large set of questions to be examined in relation to plausibility and that it is worthwhile to pursue them given that plausibility seems to be a relatively strong veracity indicator and practitioners frequently ask questions about it. We hope that this article will start research and discussions about the relationship between plausibility and veracity.
This study was funded by the Centre for Research and Evidence on Security Threats (ESRC Award: ES/N009614/1).
Cite this article as: Vrij, A., Deeb, H., Leal, S., Granhag, P. A., & Fisher, R. P. (2020). Plausibility: A verbal cue to veracity worth examining? The European
Leal et al. (2015). Experiment 2
Details refers to the total number of visual and contextual details reported during the interview.
Complications refers to the total number of complications reported during the interview.
Plausibility refers to the plausibility ratings of the interview.
Participants were or were not exposed to a Model Statement.
Leal et al. (2019)
Details refers to the total number of visual and contextual details reported during the interview.
Complications refers to the total number of complications reported during the interview.
Plausibility refers to the plausibility ratings of the interview.
Verifiable sources refers to the total number of verifiable sources reported during the interview.
Participants were or were not exposed to a Ghostwriter or Be Detailed condition.
Vrij, Leal, Deeb, et al. (2020). Experiment 2
Details refers to the total number of unique details reported throughout the different parts of the interview.
Complications refers to the total number of unique complications reported throughout the different parts of the interview.
Plausibility refers to the plausibility ratings of the entire interview.
Verifiable sources refers to the total number of unique sources reported throughout the different parts of the interview (witness and digital sources combined).
Participants were or were not exposed to a Model Statement and were or were not given an Information Protocol.
Vrij, Leal, Fisher, et al. (2020)
Details refers to the total number of unique details reported throughout the different parts of the interview.
Complications refers to the total number of unique complications reported throughout the different parts of the interview (complications ‘low’ and ‘medium/high’ combined).
Plausibility refers to the plausibility ratings of the entire interview.
Participants were or were not given information to read about the Model Statement technique or the dependent variables ‘complications’, ‘common knowledge details’ and ‘self-handicapping strategies.
Deeb et al. (2020)
Details refers to the total number of unique details reported throughout the three interviews (core and peripheral details combined).
Complications refers to the total number of unique complications reported throughout the three interviews.
Plausibility refers to the plausibility ratings of the three interviews combined.
Participants were or were not asked to sketch while narrating.