Between 2002 and 2015, ISIS was either directly or indirectly responsible for terrorist attacks that killed more than 33,000 people and wounded 41,000 more, according to a new analysis from the National Consortium for the Study of Terrorism and Response to Terrorism.

It’s a startling figure. If attacks with unknown perpetrators are excluded, this means that ISIS bore responsibility for 13 percent of terrorist attacks globally during that period, with 26 percent of all terrorist attack deaths, 28 percent of injuries and a further 24 percent of kidnap victims.

These figures include not only acts committed by the core ISIS group, but also the precursor groups that came before it was officially founded — primarily al-Qaida in Iraq — as well as the affiliates and individuals inspired by ISIS who came after.

Erin Miller, a researcher with START with the University of Maryland and the author of the report, notes that while this is clearly a significant chunk of terrorist attacks, there may be significant overlap in the early years with al-Qaida, a former ally of ISIS that is now its most important rival. Additionally, as the START database is based on news reports, some terrorist attacks may be missed — especially older terrorist attacks or those within war-torn countries such as Syria.

However, the analysis does point to a number of interesting details. It finds, for example, that until April 2013, almost all attacks (95 percent) by ISIS predecessors were carried out in Iraq. After that, the leader of what was then known as the Islamic State of Iraq announced an expansion of his group to include al-Nusra Front in Syria, though al-Nusra later disavowed this.

April 2013 now seems to mark the beginning of the expansion of attacks by ISIS, with an expansion not only in geographic scope but also the number of attacks and their violence. Between 2013 and 2015, START found that there were 32 occasions on which more than 10 Islamic State attacks were carried out in a single day. All of these occasions took place in Iraq.

What has made less of an impact, despite some high-profile attacks, is the work of individuals inspired by ISIS but with little to no official link to it. While there has been much attention paid to the work of so-called “lone wolves” who carry out attacks in ISIS’s name, the analysis found that between 2002 and 2015, they made up less than 1 percent of all attacks.

Generally, these attacks took place in areas where ISIS itself was unable to easily operate. Eight of these attacks took place in the United States and six in France, for example. The START analysis found that nearly two-thirds of the weapons used in these attacks were firearms.