New Study Links Fatigue, Police Racial Bias

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Police officers show significantly greater evidence of unconscious racial bias when they’re fatigued, according to a newly reported study by a researcher at Washington State U. in Spokane.

“When officers received less sleep preceding each test session, they were significantly more likely to associate Black Americans with weapons compared with when they had received more sleep. In other words, sleep restriction appeared to increase anti-Black bias,” writes Dr. Lois James, an assistant professor who conducted the study. James specializes in exploring the relationship between sleep and performance in LEOs, military personnel, combat medics, and other “elite” populations.

The finding, she says, has “important implications for police training” and for “the current climate of police-citizen unrest.”


Across an 18-month period, James subjected a pool of 80 volunteers from a medium-size municipal PD (about 290 sworn) to four separate sessions of image-association tests. For the week immediately before each session, the officers’ sleep was monitored by a wristwatch-like device that objectively measured their individual “quantity, timing, and quality” of sleep.

On test day, the officers—predominately white males from all shifts with an average of 15 years on the job—individually faced a computer screen while pictures of white and black faces randomly appeared. Among these pictures, images of inanimate objects also appeared. Some objects were innocuous (wallets and cell phones, for example), but others randomly interspersed were weapons—handguns, shotguns, rifles, knives.

Once the object appeared, the officer was to press a button indicating whether it was a weapon or something non-dangerous. During a typical session of about 10 minutes, James told Force Science News, an officer would see approximately 100 faces, equally divided between black and white, and approximately 200 object images, equally divided between weapons and innocuous objects.

The officers were scored as to response time and accuracy: how fast did they decide whether an object shown was a potential threat and how often were their conclusions correct.


Analyzing the results, James found that a strong majority of the officers tended to more quickly associate what they believed were weapons with black faces and were more often wrong in assessing innocuous objects as weapons when black faces were involved. These are considered valid indications of moderate to strong unconscious or “implicit” racial bias, she says.

A “large body” of similar findings have been reported from other studies as well. Indeed, implicit biases exist outside their conscious awareness “in people across many walks of life,” James writes, by no means just in cops.

But her study emphasizes two other discoveries:

  1. The degree of measured bias, ranging from none to strong anti-black bias and including even some anti-white bias, fluctuated significantly within individual officers across the four test sessions.

    This suggests that “implicit bias is a variable state, not a stable trait,” James writes, and thus “may well be susceptible to change.”

  2. Sleep and bias were significantly linked.

According to the wrist monitors, officers slept an average of about 7 hours per 24-hour period in the week before each test session. The range was broad, though, from 2.5 hours to 14.5 hours—and meaningful. The officers “displayed more anti-Black bias when they had received less sleep” before the tests, James writes.

This is similar to findings from a study by other researchers who tested resident physicians working in a hospital ER. They found that “implicit racial bias against Black Americans increased from preshift to postshift when the emergency department was particularly busy,” James writes, suggesting that and “internal stressors” like fatigue can have a definite attitudinal impact.


“The findings that bias is variable and also that sleep restriction increased anti-Black bias have implications,” James writes. “Specifically, if implicit racial bias is susceptible to change, then training designed to reduce bias is not doomed to failure. Furthermore, if tired officers are more biased, then programs designed to improve officer sleep may have consequences beyond improving officer health.”

Anti-bias training for police is needed, James writes. But just what constitutes the most effective training remains uncertain, she says. She hopes to shed light on that question through a three-year study she’s launching in January with 400 officers from Cleveland (OH) PD.

One-quarter of the participants will be assigned to each of four groups: a control group that receives no anti-bias training; a group that receives classroom training in detecting and managing implicit bias; a group that is trained using a unique anti-bias simulator program James principally designed, which we described in Force Science News #328 (1/10/17); and a group trained with both classroom and simulator methods.

“The goal,” she says, “is to identify best practices for reducing bias, leading to improved police decision-making and enhanced citizen trust.”

NOTE: In an interview with FSN, James stressed that evidence of implicit bias in officers does not necessarily translate into biased behavior on the street. In practice, officers appear able to “override” innate feelings of bias with professional conduct. In a previous FSN,  in fact, we described her results in an earlier study that found “officers were less likely to erroneously shoot Black suspects and were slower to shoot when faced with Black compared with White suspects.”

FSI’s executive director Dr. Bill Lewinski, who was not involved in James’ research, agrees that her laboratory findings should not be seen as predictive or reflective of decisions made in real-life encounters.

“It’s true that fatigue can influence judgment, usually in a negative fashion,” he told FSN. “But an officer’s decision to use force is a complex phenomenon, shaped by many variables including ‘priming’ information received from dispatch, contextual cues, past experience, furtive suspect movements, and so on. More research is yet to be done before we have definitive answers about decision-making under stress.

“Still, this is an important study that broadens our insights about the impact that sleep deprivation and fatigue have on the law enforcement profession.”

James’ current study, “The Stability of Implicit Racial Bias in Police Officers,” appears in the journal Police Quarterly and includes detailed descriptions of other research and findings regarding this phenomenon. click here for a free abstract and a link for ordering the full study for a fee.

Dr. James can be reached at WSU’s Sleep & Performance Research Center at: lois_james@wsu.edu.

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