(NewsNation) — The FBI’s new annual crime report released Wednesday found a 4.3% increase in the total number of murders in 2021, but experts warn the estimate draws on fewer data points than previous years.

After spiking nearly 30% in 2020, the rise in homicides continued in 2021. The FBI estimates there were 22,900 homicides nationwide last year, up from 22,000 the year prior.

Overall, violent crime decreased about 1% from 2020 to 2021, the report found. Much of that is attributable to an 8.9% decrease in the robbery rate.

But the latest data comes with an important caveat.

“It is important to note that these estimated trends are not considered statistically significant by NIBRS estimation methods,” the FBI said in a press release. “The nonsignificant nature of the observed trends is why, despite these described changes, the overall message is that crime remained consistent.”

The statistics are based on estimates derived from data submitted by local law enforcement agencies but due to changes with the FBI’s reporting system, experts say fewer agencies participated this year.

“One-third of police departments in the United States did not submit any data to the FBI at all, making this year’s crime data estimates far less certain than they usually are,” said Laura Bennett, a public safety researcher at the Center for Just Journalism.

This year’s report draws on data from just 11,800 of the more than 18,800 law enforcement agencies nationwide. As recently as 2018, more than 16,000 agencies were submitting data.

The notable ommissions include two of the largest police departments in the country. The New York City Police Department (NYPD) and the Los Angeles Police Department (LAPD) did not submit their 2021 crime data to the FBI.

The federal agency says its the first year all crime estimates are based on the National Incident-Based Reporting System (NIBRS), which the FBI says will provide more detailed data moving forward.

“NIBRS goes much deeper because of its ability to provide circumstances and context for crimes like location, time of day, and whether the incident was cleared,” the agency’s website reads.

That system requires time and money to implement and for that reason, experts say, it could be a few years before local agencies have the necessary resources to report complete data.

Crime continues to be a top issue for Americans across the country. Nearly one in five registered voters say crime is their biggest issue to vote on rather than inflation, unemployment and COVID-19, according to a NewsNation poll released earlier this week.