The FBI said on Monday that the number of U.S. police departments reporting hate crimes plummeted last year as it shifted to a new crime reporting system, but participating agencies continued to report an overall increase in hate crimes.

In its closely watched annual hate crime report, the FBI said about 4,000 of the nation’s more than 18,000 law enforcement agencies did not report any hate crime last year, lowering police departments’ rate of participation in the FBI’s data collection to nearly 65% from 93% the previous year.

The FBI’s annual report is widely used as a broad measure of hate crimes in America. The sharp drop in the number of police agencies reporting data to the agency makes it difficult to tell whether hate crimes rose or fell last year even as other data indicate an overall upward trend.

Asked whether the report renders any year-on-year data comparisons meaningless, an FBI official said, “Until we see an increased participation for the law enforcement agencies and recognizing this is a transition year, that would be correct.”

The new FBI report shows there were 7,262 hate crime incidents in the United States in 2021. By comparison, 2020 saw 8,263 incidents.

But comparing the two figures is inexact because they are based on different datasets.

“When we’re seeing decades-old records being broken in major cities and numerous states, having one-third of agencies not participating at all in the FBI report means we simply do not have an accurate official picture of what is actually happening nationally,” said Brian Levin, director of the Center for the Study of Hate and Extremism at California State University, San Bernardino.

Any increase in hate crime was “erased by a lack of participation,” Levin said.

The FBI said that despite a drop in police agency participation in its new system, participating law enforcement agencies continued to report an overall increase in hate crime.

“Although the hate crime statistics reported to us are lower in 2021, hate crime statistics overall are not decreasing, meaning of the agencies that are reporting to us, they are reporting an increase in hate crime,” an FBI official said during a press call ahead of the report’s release.

The FBI’s new crime reporting system, called the National Incident-Based Reporting System, or NIBRS, offers more granular details and context about crime, which the bureau says will allow police agencies to better fight crime.

But the downside is a lower participation rate by police agencies struggling to make the switch. FBI and Justice Department officials said they’re working to improve participation through training and other initiatives.

The low level of hate crime reporting echoes a similarly low rate of participation in the FBI’s report on overall crime released in October.

In that report, the FBI said 63% of all law enforcement agencies reported crime data for 2021, the lowest level of participation in more than four decades.

The FBI defines hate crime as a criminal offense “motivated, in whole or in part, by the offender’s bias(es) against a race, religion, disability, sexual orientation, ethnicity, gender, or gender identity.”

Hate crimes have been on an upward trend in recent years.

Last year, the FBI reported that hate crimes rose to their highest level since 2001 when the September 11 terrorist attacks fueled a surge in attacks against Muslims and others perceived as Muslims.