For the past 40 years, more than half of all police-involved deaths in the U.S. have gone unreported, a new study published by the peer-reviewed journal Lancet found. Researchers at the University of Washington School of Medicine’s Institute for Health Metrics and Evaluation found that over 55 percent of police killings between the years 1980 and 2018, which amounts to over 17,000 deaths; were either misclassified or unreported.

Furthermore, the study found that Black Americans are more likely than any other group to die by police violence — 3.5 times more likely than white Americans.

“Recent high-profile police killings of Black people have drawn worldwide attention to this urgent public health crisis, but the magnitude of this problem can’t be fully understood without reliable data,” Fablina Sharara, a researcher at the University of Washington School of Medicine and co-lead author of the study, told The Guardian.

Researchers compared data from the U.S. National Vital Statistics System (NVSS), a government database that tracks the U.S. population, with non-governmental, open-source databases, such as news reports and public record requests that provide a wider scope of police brutality.

“Open-sourced data is a more reliable and comprehensive resource to help inform policies that can prevent police violence and save lives,” Sharara said.

According to the report, the NVSS database misclassified almost 60 percent of instances where police officers killed Black Americans. The database also failed to report around 50 percent of police fatal encounters with Hispanic people; 56 percent of police deaths involving non-Hispanic white people and 33 percent of deaths involving other races.

The erroneous reporting is critical, because “inaccurately reporting or misclassifying these deaths further obscures the larger issue of systemic racism that is embedded in many U.S. institutions, including law enforcement,” Sharara said.

The study also pointed to areas where a conflict of interest could lead to misreporting. For example, coroner offices are often part of local police departments, which could disincentivize them from saying a death was caused by a cop.

“The same government responsible for this violence is also responsible for reporting on it,” Sharara said.

All in all, the study found that a recorded 30,600 men and 1,420 women have been killed by police officers in the U.S. from 1980 to 2019.

“As a community we need to do more. Efforts to prevent police violence and address systemic racism in the USA, including body cameras that record interactions of police with civilians along with de-escalation training and implicit bias training for police officers, for example, have largely been ineffective,” the study’s co-lead author Eve Wool said.