How many gang members are in the United States? It depends who you ask, and what political party they affiliate with.

In his State of the Union speech this January, President Donald Trump called one such gang, the MS-13 as “worse than Al-Qaeda” and “true animals.” The Trump Administration believes that there are more than 10,000 MS-13 gang members in the US as a result of lax immigration policies and they have used that claim to remove protections from some 700,000 Dream Act beneficiaries who are now at risk of deportation.

The official federal definition of a gang is “a group or association of three or more persons” who “engage in criminal activity that creates an atmosphere of fear and intimidation.” But in practice, the definition of a gang varies from state to state and city to city.

Meena Harris, director of the federally-supported National Gang Center, says in a FiveThirtyEight article:

“There’s no universal definition of gang, and the debate still continues over what constitutes a gang and a gang member.”

Who gets counted as a gang member — and whether those counts include people who are not identified as members of gangs but who are associated with a gang2 — can vary from state to state, department to department, and even officer to officer. “What’s accurate and what’s not accurate really depends on the level of training for the police officer,” Harris said.

Adding to the murkiness of gang data is the sloppiness of reporting from the police at state and city levels. Some report gang numbers. Others do not. And the number of reporting police departments varies from year to year. In New Orleans, for example, police said there was zero gang killings in 2015 even though there was a city report that attributed 49 murders that year to gangs. A similar situation was reported in Baltimore in 2016.

More from FiveThirtyEight:

The way agencies report and store gang membership information in databases can cause additional problems. A 2016 audit of the California gang database CalGang,3 for example, found that “agencies have failed to ensure that CalGang records are added, removed and shared in a way that maintains the accuracy of the system and safeguards individuals’ rights.” In another case earlier this year, problems associated with gang designations led the police department in Portland, Oregon, to stop identifying people as gang members.

The only attempt at a comprehensive count of gang members ended in 2012 when the budget for the National Youth Gang Survey was cut. The survey’s last count was 850,000 members in 30,700 gangs across the United States.