Truthfulness Bias: What It Is And How It Affects Our Perception

Truth bias

Have you ever heard of truthfulness bias? It is a phenomenon with two possible meanings: on the one hand, it is the tendency to believe that others are honest and therefore tell the truth, and on the other, it is the tendency to remember “false” information as true.

In this article we bring you the findings of scientific research for each of these two meanings, since the phenomenon of truthfulness bias has been studied in both ways. As we will see, this is a concept closely related to criminal investigation and legal psychology. But why? Let’s find out.

Truthfulness bias: two meanings

First of all, we must keep in mind that truthfulness bias has two possible meanings.

1. Meaning 1: Believing that others are honest

The first meaning of truthfulness bias, a term introduced by Zuckerman et al. in 1981, is the one that defines it as the tendency we have to believe or assume that other people are honest (and that they tell the truth, that they are sincere).

That is, according to the truthfulness bias, we would assume that others are honest much more than they actually are.

2. Meaning 2: Remembering “false” information as true

The second meaning of truthfulness bias, which has been recently investigated in a study by Pantazi, Klein & Kissine (2020), refers to the fact that people We tend to mistakenly remember as true information that has been explicitly explained to us to be false..

That is, according to this bias, we tend to remember information labeled as “false” as true. Sounds a bit contradictory, doesn’t it?

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Scientific investigation of both phenomena

But what exactly does scientific research say about truthfulness bias? We are going to analyze the research that has been carried out in relation to this phenomenon, differentiating the two meanings attributed to it.

1. Truthfulness bias 1: believing that others are honest

What does research suggest when analyzing truthfulness bias, understood as the “excessive” belief in the honesty of others? Are we good at detecting lies?

According to a study by Levine, Park and McCornack (1999), we tend to identify truths more easily than lies.

But why? According to the authors, precisely because we manifest this truthfulness bias, and we tend to consider that others generally tell us the truth; This would explain why our accuracy when judging truths is good, and when judging lies, it is a little worse (Levine et al., 1999; Masip et al., 2002b).

In subsequent studies, specifically in a meta-analysis carried out by Bond and DePaulo, it was found that the average % of truth judgments was 55% (by chance, this % is expected to be 50%, that is, the average went up). This % made the judges’ accuracy when judging statements as true reach up to 60%. This last percentage was slightly higher than that which appears when judges had to judge false statements (which stood at 48.7%).


We have talked about judges, but what about police officers? According to the research of Meissner and Kassin (2002), Bond and DePaulo (2006) and Garrido et al. (2009), in police officers this trend that we have explained is reversed, and it is observed how in most cases the precision in detecting false statements is higher than the precision in detecting true statements.

The Mendacity Bias

A possible explanation for this is that Police officers have a greater tendency to make false judgments and not so much truth judgments; In other words, they show mendacity bias. How is this bias defined? It consists of the tendency to make more false judgments than true ones (which is true among police officers).

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In non-professional people (that is, neither judges nor police nor belonging to the legal sector), however, this bias does not appear, since according to research (Levine, Park and McCornack, 1999) we would tend to be more precise when it comes to of judging truth rather than lies (i.e., the mendacity bias is reversed).

2. Veracity bias 2: remembering “false” information as true

Studies prior to Pantazi et al. (2020), already mentioned, reveal that People, by themselves, are biased by the truth; This means that we tend to believe information we receive, even when it is marked or labeled as false information.

According to the study by Pantazi et al. (2020), the truthfulness bias consists of a type of inefficiency that people present when calibrating the quality of the information provided to us by the medium, which also affects when “correcting” said information.

Study development Pantazi et al. (2020)

To demonstrate the truth bias, the experimenters of the study we discussed proceeded as follows: they designed an experimental paradigm where Mock jurors (condition or study 1) and professional jurors (condition or study 2) were asked to read two crime reports.

These reports contained information that aggravated or mitigated such crimes, and it was explicitly specified that this information was false.

What they evaluated in the study was: the decisions made by the juries in relation to the cases presented (that is, the sentences), including how false information influenced them, as well as their memory (and, obviously, also how false information affected it).

In short, we wanted to check if the truth bias appeared in these groups, in the legal context in which the aforementioned study is framed.

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What do the findings of this experiment suggest regarding truthfulness bias?

Basically, that Both mock jurors and professional jurors exhibited truthfulness bias; This means that all participants had made decisions, in relation to the cases, biased by false information, and that their memory was also biased by said information (false information).

Specifically, the results of condition or study 2 (professional jury) indicated that professional judges had been affected (or influenced) by false information when issuing their verdicts, in a similar way to what occurred with the study 1 (mock jury). That is, to a similar degree.

On the other hand, it is also true that considerable variability was detected in the judges’ decisions, once the false information was heard, in relation to the years in prison they proposed for the accused (across the different cases).

Furthermore, the results of the study reveal that 83% of the time, judges issued longer sentences after receiving false information or evidence that aggravated the crimethan when they received false evidence (and not so much information).


What did you observe in the judges regarding the memory evaluated? The results show how juries, both simulated and professional, showed a tendency to erroneously remember aggravating information that was explicitly false.

A curious fact that the study reveals is that the judges’ ability to filter or discriminate false information from false information (whether we analyze their decisions and sentences, or their memory), did not depend on their years of experience.

Bibliographic references:

Garrido, E., Masip, J. and Alonso, H. (2009). The ability of police officers to detect lies. Journal of Criminal Law and Criminology, 3 (2), pp. 159-196. Levine, TR, Park, H.. S., & McCornack, SA (1999). Accuracy in detecting truths and lies: Documenting the “veracity effect.” Communication Monographs, 66, 125-144. Masip, J., Garrido, E. & Herrero, C. (2002). Yearbook of Legal Psychology. McCornack, SA & Parks, MR (1986) Deception Detection and Relationship Development: The Other Side of Trust. Pantazi, M., Klein, O. & Kissine, M. (2020). Is justice blind or myopic? An examination of the effects of meta-cognitive myopia and truth bias on mock jurors and judges. Judgment and Decision Making, 15(2): 214–229.