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

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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-Qaeda, a former ally of the Islamic State 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 Islamic State predecessors were carried out in Iraq. After that date, 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 the Islamic State, 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.

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There was a further expansion in mid-2014, with groups who had sworn allegiance to the Islamic State now carrying out attacks in their name. The biggest increase came in March 2015, when Boko Haram, an insurgency in Nigeria, pledged its allegiance to the Islamic State. This group, already well-known for extreme violence, added a considerable number of attacks to the Islamic State's tally — almost 400 attacks that killed more than 4,000 people (including more than 1,000 attackers), according to START. Recent developments suggest that their relationship with the Islamic State's core is complicated and perhaps strained, however.

What has made less of an impact, despite some high-profile attacks, is the work of individuals inspired by the Islamic State 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 the Islamic State'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 the Islamic State 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.

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START's analysis also notes that the type of violence conducted by the Islamic State and its allies seems to differ from other terrorist attacks. Attacks by the Islamic State tend to be deadlier — 74.7 percent of Islamic State attacks were lethal during the period, versus 51.4 percent of non-Islamic State attacks; on average, 7.3 people died per Islamic State attack versus 2.1 in other attacks. Islamic State attacks were also more likely to use suicide tactics or take hostages, and the Islamic State coordinated attacks 38.5 percent of the time versus 13.3 percent of the time for non-Islamic State attacks.