People who have faces that are judged as less trustworthy are given the death penalty more often than people viewed as trustworthy, according to recent research in the journal Psychological Science. The results “paint a somewhat alarming picture of how systems of legal punishment are vulnerable to the same biases in person perception that afflict everyday individuals,” write John Paul Wilson and Nicholas Rule, the authors of the paper.

This study builds on previous research suggesting that people judge the trustworthiness of faces with a high degree of consensus—we more or less agree on which faces count as trustworthy and which don’t.

People with less trustworthy faces are, unsurprisingly, less likely to be trusted by other people. Economic games played in psychology labs show that even children as young as five years old are less likely to trust these individuals, and that this effect holds even when there's information about the other person suggesting that they’re trustworthy.

Previous studies on how this might affect criminal judgements have focused on hypothetical scenarios where participants are shown pictures of faces and asked to guess whether each person could be guilty of a certain crime. This suggested there could be a real-world effect, but it hadn’t yet been confirmed.

Face determines fate

Wilson and Rule decided to use pictures of people currently incarcerated in the state of Florida, which still has the death penalty. They took pictures of 371 men on death row (almost the whole population, barring a handful eliminated for a variety of reasons) and matched them to men serving a life sentence for first degree murder. The researchers edited the pictures to grayscale to block out any colour cues from the men’s uniforms (standardly blue, but orange for death row).

The pictures were then shown to participants in an online study using Amazon Mechanical Turk. Because there were so many photos, the 742 pictures were divided into seven sets, with each set being rated by approximately 30 people.

Participants were asked to rate each picture as trustworthy or not, on a scale of 1 to 8. Separate groups of people on Mechanical Turk were asked to rate the same photos for other features, like attractiveness and facial maturity.

The results showed that trustworthiness ratings were linked to the type of sentence each prisoner had. Those individuals with a death sentence had an average rating of between 2.73 and 2.79 out of 8, while those with a life sentence had a slightly higher average rating of between 2.84 and 2.9.

The difference was very small, but significant according to statistical tests. It’s possible that even a small drop in perceived trustworthiness could be enough to push a sentence from life to death. The ratings were also all on the low side compared to the general population. It’s not clear whether the people rating the photos knew they were looking at pictures of actual convicts; if they did, it probably explains why the ratings were so low.

Once ratings for other facial characteristics like attractiveness and maturity were accounted for, the difference became more significant. This suggests that, in line with previous research using hypothetical scenarios, the trustworthiness of the inmates’ faces could have played a role in the kind of sentence they were given, and that other facial characteristics influence perceptions as well.

Sometimes the cover is a good guide to the book

But what if people with less trustworthy faces committed more heinous crimes, and that’s why they were sentenced to death? We can't just assume that facial structure has no relationship to behaviour—it still needs to be tested. If people judge characteristics like trustworthiness with a high degree of consensus, it might be because we’ve learned that people with a certain kind of face are actually less trustworthy.

There is a limited amount of evidence to suggest that certain facial characteristics might actually be connected to behaviour: one small study has found that men with wider faces are more likely to show aggressive behaviour, and more likely to be judged as aggressive by other people.

There isn’t the same evidence for trustworthiness, though. A paper reporting multiple studies found that people didn’t judge the faces of military or corporate criminals as any less trustworthy than the faces of military heroes or noncriminal executives, and that people with faces judged as less trustworthy were no more inclined to cheat on a test.

To explore this possibility, Wilson and Rule found pictures of men who had been convicted of murder and sentenced to death or life, but later exonerated of the crimes and released. They eliminated anyone sentenced to life who was from a state where the death penalty hadn’t been an option. This left them with 20 people sentenced to life in prison, and 17 sentenced to death.

After running a similar study on Mechanical Turk, this time with just 39 people in the main group (additional groups again rated other characteristics like attractiveness), they found once again that less trustworthy faces were more likely to get the death penalty. This time, adding the other features in didn’t help, which could suggest that with a sample size this small, the results were just noise.

Aside from the small sample size, there are other flaws and limitations: exoneration doesn’t necessarily mean the person didn’t commit the crime in question, any more than conviction of a crime means that they did. Because of this, using exoneration as a proxy for not being guilty is potentially inaccurate.

The authors also didn’t look at any of the details of the crimes committed by the inmates in the first study, who were still in prison. This information could have given more insight into whether those sentenced to death did actually commit more heinous crimes.

Nonetheless, this study corroborates past research, finding an effect in the real world that previously had only been seen in hypothetical games in the lab. Replication with other samples is needed before anyone draws firm conclusions, but the direction that multiple studies are pointing towards is troubling, to say the least.

Psychological Science, 2015. DOI: 10.1177/0956797615590992 (About DOIs).