The mass shooting in a church in Sutherland Springs, Texas, on Sunday added 26 deaths to a year of violence across the country, from a Las Vegas concert to the Fort Lauderdale, Florida, airport. According to data from multiple sources, shootings like these are claiming more lives than they have at any point in the last 35 years.

Information on mass shootings is notoriously hard to acquire, in part because the federal government does not provide funding for gun violence research. But in the absence of good, up-to-date official government data, other entities have stepped in. The magazine Mother Jones, for example, keeps a database of all incidents where four or more victims are killed in a public space, excluding deaths that came as part of crimes like a robbery or gang violence. The Mother Jones database goes back to 1982, and mass shootings in the last few years have resulted in more total fatalities than ever.

Because Mother Jones relies on news reports to gather information, it’s possible that the magazine’s database missed some incidents, which is especially likely for shootings that happened further in the past or resulted in a relatively small number of casualties — the media might be less likely to report on these incidents, and what coverage there is might be harder to find. Conversely, there are likely fewer gaps in the database after 2012, when the project was launched and the magazine began periodically updating the data. If that’s true, the exclusion of some older shootings could be one explanation for the spike in deaths in recent years. But if we focus only on the deadliest mass shootings — those with 10 or more deaths, which are much more likely to be covered by the media — it’s still clear that the there has been an increase in fatalities since 1982:

And while decreased press coverage might explain why fewer deaths from decades ago appear in the database, the Mother Jones data shows a spike in fatalities even in just the last five or 10 years, when we would expect news outlets to cover the vast majority of such shootings.

In addition, other surveys of these incidents show a similar trend. Data from a Stanford University project called Mass Shootings in America defines a mass shooting much more broadly than Mother Jones does, but the project’s data shows the same significant increase in deaths whether you focus on all incidents or only the most deadly.

And an article published by Politico last month that used a third source of data on mass shootings found that the number of fatalities is increasing even after adjusting for the rise in the U.S. population. That Politico article pins the blame on more deadly mass shootings, rather than an increase in the number of shootings. In contrast, the Mother Jones database shows both an increasing number of mass shootings and more fatalities per attack.

The reasons for the skyrocketing number of fatalities resulting from mass shootings are not well understood. There is evidence that the high number of guns in the U.S. contributes, and the timing of the increase roughly coincides with the expiration of the assault weapons ban in 2004. It’s possible that the increasing availability of previously banned items like high-capacity magazines allows shooters to gun down more people than before. But research on the ban is equivocal about its effects on crime in general, and little research has been done on mass shootings in the U.S. in particular.

Regardless of the cause, the spike in deaths in mass shootings is significant enough to register on the national homicide rate. The Stanford database shows an additional 80-100 deaths per year in 2015 and 2016 compared to a decade ago, which would contribute about a 1 percent increase in the number of homicides nationally, and explain a little of the bump in homicides in the last few years. In other words: We may not know why mass shootings are claiming so many more lives, but the evidence is clear the problem is getting worse.