It's a scene we have become all too familiar with. What begins as a normal outing -- concertgoers listening to music, tourists enjoying a meal, travelers catching a flight -- turns into a fearsome nightmare in a matter of seconds.

The most recent attack took place in Barcelona, Spain, on a Thursday in mid-August, when a man drove a van into the crowds on Las Ramblas, a popular street known for its tourist attractions. By the time all of the suspected members of the cell were caught or killed, another attack took place in nearby Cambrils and authorities had linked a previous house explosion to the assailants. Sixteen people were killed, and more than 100 injured. ISIS later claimed the attackers were "soldiers of the Islamic State."

As a new study shows, this style of attack is a part of an increase in terrorism in Western countries inspired by jihadist ideology since June 2014, when ISIS declared a "caliphate." The report from the Italian Institute for International Political Studies (ISPI) breaks down the data to better understand what's behind attacks of this nature. First released in June 2017, it initially examined more than 50 attacks from the three years prior that were determined to be motivated by Islamic extremism.

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But a spate of attacks this summer in Europe since the report's publication have already changed the results, one of the authors, Dr. Lorenzo Vidino, says in a recent article for the BBC. There, he explained the report's findings based on new data updated through August 2017.

While far more acts of Islamic extremist terror take place in other parts of the world -- often in majority-Muslim countries like Iraq, Afghanistan and Pakistan, where thousands have been killed in such attacks -- the study focused on the impact in Western nations. It found there has been an unprecedented increase in Europe and North America in the past three years -- 63 attacks, to be exact, from September 2014 to late August 2017.

These incidents took place in nine European countries -- Spain, Belgium, France, the UK, Finland, Germany, Austria, Denmark, and Sweden -- as well as the United States and Canada. Most of these attacks happened in large cities, and in areas heavily populated with tourists or people enjoying some form of entertainment.

The study found that 424 people died, and 386 of those deaths came from just 11 of the 63 attacks. The largest, in Paris in November 2015, left 130 people dead.

But what do we know about the people carrying out these acts of terror? A majority of the 85 total assailants are men in their 20s. Only two were women. Most of them (74 percent) were known to authorities before carrying out their attacks. And two-thirds were citizens of the country they terrorized, or were in the country legally as a resident or tourist.

When it comes to determining the involvement of organized extremist groups, particularly ISIS, there is less certainty. Of the most deadly incidents, only the attacks in Paris and Brussels are thought to have been planned and carried out under ISIS leadership. The majority of the other attacks could not be directly linked to ISIS, even though the assailants often pledged their allegiance to the group. Many of them, such as the U.S. attacks in Orlando and San Bernardino, were perpetrated by "lone wolf" attackers who sympathized with the ideology but did not appear to have been in contact with the group's leadership.

But in many cases, it can be hard to know for sure. ISIS often claims responsibility for attacks even if those who did it were simply inspired by its ideology from afar. Pledging allegiance to an extremist group may help explain an attacker's motivations, but that doesn't always mean the person was directly radicalized and trained by that specific group, the researchers determined. In any case, the study points out that independent attackers can pose just as much of a threat to the public as terror organizations.

The study aims to provide insights into one of the most heavily debated topics currently on the world stage: homegrown and international terror. Through its methodical documentation and analysis of assailants' backgrounds and methods of attack, it reveals trends in terror strategy and execution that can hopefully increase awareness and help inform safety measures.

As the rapidly changing data used for the report exemplifies, the threat does not appear to be dwindling.