Terrorism, Part II

This is a continuation of an exploration of the Global Terrorism Database. Last time I mentioned the GTD codes for whether an attack was ideologically international in scope. What follows are three charts breaking down global terror attacks by this variable:

In the last few years there has been an uptick in ideologically based terrorism, alongside the overall rise documented last time. Is there a meaningful difference in the average number of deaths depending on the type of attack?

A simple t-test of the number of deaths from clearly domestic vs clearly international terrorist attacks is not significant, suggesting there is no meaningful difference. However, performing the same test against the unknown attacks does show a meaningful difference for both domestic and international attacks.  This suggests to me, assuming this is not due to problems with the data, that attacks that remain unknown are more likely to be the work of individuals or amateurs rather than professional, organized groups, and hence less deadly.

Have attacks gotten more deadly over time? Breaking the sample into pre-2001 and post-2001, there does seem to be a statistically significant difference in deaths/per attack, with attacks having grown deadlier, though not by a huge amount (I ran an analysis excluding 2001 in case 9/11 was having an outsize effect; there was essentially no difference in result):

data: subset(dat, Year < 2001)$nkill and subset(dat, Year >= 2001)$nkill
t = -4.4096, df = 147780, p-value = 1.036e-05
alternative hypothesis: true difference in means is not equal to 0
95 percent confidence interval:
-0.3717482 -0.1429688
sample estimates:
mean of x mean of y
2.215667 2.473026

Now for the United States. First, the raw number of deaths from terrorist attacks. I had to manually cut off the graph, because otherwise the deaths from 9/11 would totally swamp all the other data.  We can see that there has been an uptick in recent years, though it doesn’t appear much different from what was occurring in the 70s.


What kinds of attacks are these? (Note that again I limited the y-axis).


The difference is that the attacks in the 70s were definitely domestic (think the Weather Underground), whereas the ones of late are of uncertain origin. Since 9/11, however, there have been no deaths from an outside based terrorist group. (One aside, it’s strange to me that the Oklahoma City bombing is coded as an unknown ideology). Also, while there has been a rise in the last few years, it must be noted that this number is dwarfed by the number of people killed in car accidents, accidental gun deaths, or drug overdoses.

Now these days, when people think of terrorism, they overwhelmingly associate it with jihadism or other kinds of Islam-linked extremism. (Indeed, the new Trump administration has elected to focus their domestic counter-terrorism efforts solely on Islamic extremism). Is this fair? That is, how much terrorism is actually associated with Islam?

Of course, this is a very difficult question to answer. It requires untangling complex aspects of identity, such as religion, ethnicity, and culture. Was the Irish Republican Army a ‘Catholic’ terrorist group? The Ulster Defence Association a ‘Protestant’ group? Both groups were composed of members of those respective religions, but it seems hard to say there were particularly ‘Catholic’ or ‘Protestant’ aspects to their terrorism. As such, groups like the mujahideen, who fought the Soviet occupation of Afghanistan, would not seem to be fundamentally ‘Islamic’, though they were composed of Muslims.

That being said, there is obviously a stain of terrorism, like that pioneered by Al-Qaida, that is rooted in a radical vision of the meaning of Islam. I’ve a cursory attempt at separating out such groups for analysis. The GTD codes for the perpetrating group, if known. I created two groupings: the first consists of attacks made by groups with a name matching any of several keywords associated with jihadism, such as ‘Al-Qaida’, ‘Islamic State’, ‘Al-Shabaab’, etc. I did not include Palestinian based groups, because generally the dominant goal of such groups is politically related. The other grouping is everything else, with the additional exclusion of unknown and unaffiliated groups.

Assuming my groupings were close to correct, we see that organized jihadist terrorism didn’t become a significant player until the early 90s, though it was still dwarfed by other kinds. But since about the mid 2000s, the two have moved in tandem, and are currently equal. However, in the second figure you can see this is very sensitive to the inclusion of the most terror-ridden nations: removing Iraq and Syria, the level of jihadist terrorism goes down significantly; removing Afghanistan lowers it even further. The situation in these countries, having been destabilized by civil war, may be distortive in understanding global trends.


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