survival of the fittest why terrorist groups endure

8/17/2019 Survival of the Fittest Why Terrorist Groups Endure

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Survival of the Fittest: Why Terrorist Groups Endure

by Joseph K. Young and Laura ugan

Abstract

Why do terrorist groups endure? This question is relevant to scholars and policy makers alike. In the past,

this issue has not been addressed in a systematic fashion. Recent work investigates this question using data

on transnational groups and nds that factors associated with the home country can in!uence the group"s

endurance #pplying the theory of outbidding to terrorist group survival, we argue that strategic competition

among groups predicts group duration. $sing the %lobal Terrorism &atabase, we develop a dataset using

the terrorist group as the unit of analysis to model the duration of group activity and thus include the largest

sample of groups yet. 'ontrolling for previous e(planations of both group duration and terrorism, we nd a

robust e)ect for the impact that group competition has on terrorist group survival.

Keywords* +rganisations, decisionmaking, quantitative analysis

Introduction

Why do some terrorist groups endure? While this question is certain to interest policymakers and scholars, it

has received little systematic investigation. Several scholars [1] have investigated why terror groups end,

usually focusing on specic actions !y the state or !y organisational dynamics and decline. "hese studies

have either only e#amined groups that end [$] or do not provide systematic investigation of the topic [%][&].

'sking why terror groups endure relates to understanding the environment that is conducive to groups that

use terrorism. (n short, we seek to understand why some groups who use terrorism survive for &) years

while others last fewer than &) days.

*ecent work demonstrates that the capa!ilities of the organisations [+] and the states in which they operate

[] e#plain why some groups endure longer than others. We apply the theory of out!idding [-] to this

question and argue that the strategic environment for groups aects their survival. (n short, !oth thenum!ers of competitors and where the group is in the food chain in/uences its likelihood of survival. 0inally,

we identify some alternative e#planations for terrorist group survival relating to the regime characteristics of

the state and its societal factors. 0ollowing this discussion, we dene terrorism and what constitutes a

terrorist group. We then e#plain how we conceptualie group survival. 2e#t, we discuss the research design

issues associated with modeling group survival and descri!e the data used. 'fter e#plaining data and

methods, we then discuss the results of the statistical analysis. (n the conclusion, we discuss some of the


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limitations of this particular approach to understanding terrorist group survival and suggest some avenues

for further research.

Why Some Groups Survive While Others Do Not

3ost, if not all terrorist groups end, yet we do not fully understand why. 4revious work on this question has

!een limited to case comparisons [5] or theoretical discussions without empirical tests.[6] 's 7ronin [1)]

claims, 8[t]he question of how terrorist groups decline is insu9ciently studied, and the availa!le research is

virtually untapped.: 4revious attempts to e#plain terror group survival and decline have focused on strategic

choices made !y governments and groups. "hese studies generally are single cases that fail to make large

comparisons.[11] ;sing a cross


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Outbidding and Group Survival

(t is fairly uncontroversial to state that violent groups are aected !y the competitive environment in which

they operate.[$)] Fut!idding, or the use of increased violence to attract support from a domestic

constituency, occurs where 8groups try to distinguish themselves from one another.:[$1] =loom [$$] argues

that violence is a way to 8gain credi!ility and win the pu!lic relations campaign.:[$%] While a competitive

environment may encourage terrorism, it also likely dampens group survival as other organisations drain the

pool of potential recruits. "hus, similar to interest groups operating in competitive environments, some will

succeed and some will fail.[$&] Where there are a limited num!er of groups, these organisations are

e#pected to live longer.[$+]

(n contrast, interest groups that e#perience heavy competition, using Aarwinian terms, have a higherpro!a!ility of !eing selected out. [$] Similarly, terror groups that are competing for support from

populations will survive longer in a state with fewer competing violent organisations. Gydd and Walter claim

that, 8out!idding should occur when multiple groups are competing for the allegiance of a similar

demographic !ase of support.:[$-] 7ronin concurs and argues that, 8[g]roups mayHdecline !ecause they

lose a competition for mem!ers or support with other groups.:[$5] "his competition should drive groups out

of the environment and lead to shorter life spans. 's =loom argues a!out the role of suicide !om!ing in

competitive environments, 8[a]lthough each !om!ing episode sacrices one supporter, it recruits many

more.:[$6]

=loomIs theory is focused on how intergroup competition in/uences the pro!a!ility of suicide terrorism.[%)]

We e#tend a more general logic of out!idding to terrorist group survival. 0or e#ample, =loom suggests that

the 4opular 0ront for the Di!eration of 4alestine >40D4 turned to suicide terror as a means to attract

supporters.[%1] Auring the second (ntifada, Jamas and other more violent organisations successfully

attracted more supporters threatening the 40D4Is survival. Similar to =lom!erg et al., diversifying their

tactics, attracted more supporters and thus kept the organisation alive.[%$] "he out!idding theory has a

longer history in the ethnic violenceKpolitics tradition.[%%] Fthers scholars, such as Gaufman [%&], have

applied the theory to civil con/ict. (n this formulation elites mo!ilie civilians !y appealing to more e#treme

demandsKtactics vis


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0rom this discussion, we can derive the following hypothesisE

+utbidding -ypothesisE "error groups that operate in a more competitive environment are more likely to fail.

's the discussion a!ove suggests, out!idding as an e#planation for group survival is a natural e#tension of

previous arguments. 'dditionally, arguments from organisational theory can also add some rened

e#pectations concerning how certain kinds of groups are more likely to fail than others.

*egardless of the nature of the organisation, Jannan and 0reeman >1656 citing Stinchcom!e >16+ suggest

8that organisations face a lia!ility of newness: or that the failure rates of new groups should !e higher than

for esta!lished groups. 2ew organisations are particularly vulnera!le as their mem!ers are strangers or at

least not properly trained or had enough time to !uild trust among their participants.[%-] 's =aum and

3eias argue in a study of hotel competition in 3anhattan, if organisations are in a population are not equal

competitors, a count of the num!er of organisations alone may not adequately measure competition amongthe groups.[%5]

(n our case, a count of terrorist organisations may not !e enough to e#plain why certain groups fail more

readily than others. *esource dependence is also another important predictor of organisational failure.[%6]

Darger rms and rms with greater resources are e#pected to survive in an industry longer and the empirical

evidence conrms this claim.[&)] "o generate terrorist violence requires resources. (f we assume that

groups that are more violent, e#perienced and thus potentially drawing more resources have an advantage

in the market, then we can dierentiate these groups from less violent groups. (n sum, these characteristics

likely separate organisations that are new competitors with industry Top &ogs.

"errorist groups similarly operate in these competitive markets with dierentials in sie, starting point, and

resource endowments.[&1] While the num!er may matter, we e#pect that !eing the dominant group in the

market may reduce the risk of failure as compared to !eing newerKless dominant in the market. (n Sri Danka,

for e#ample, during the late 165)s many groups vied to represent the "amil community in their goal to

achieve an independent state from the Sinhalese maMority. 's =loom highlights, the Di!eration "igers of "amil

Belam >D""B systemically eliminated other competitors and !y $))$ was the sole organisation !argaining

with the Sri Dankan state.[&$] "he D""B was advantaged over rivals as they had greater resources through

local ta# e#traction as well as diaspora support disadvantaging competitors and increasing their pro!a!ly.

3ost importantly, the D""B was the dominant non


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(n addition to this linear hypothesis, !ased on the a!ove discussion, we also e#pect that "op Aogs are less

likely to fail as they e#perience more competition. 's the num!er of groups increases, we e#pect that "op

Aogs are less likely to fail as compared to their competitors.

(n the 4alestinian market for violent organisations, Jamas or the 4DF may !e the "op Aog depending on the

year. "heir pro!a!ility of survival may actually increase as the num!er of competitors increases. Smaller

groups, such as Cund al


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"o date, one of the most comprehensive studies of how terror groups end and what states do to encourage

this process is a study from the *and 7orporation.[+1] Cones and Di!icki amass a data!ase of over ))

groups and e#amine the descriptive statistics to e#plain why some groups end and others do not. While this

study moves !eyond case analysis or comparison, they fall short of estimating regression models to control

for alternative arguments.[+$] Cones and Di!icki identify eight ways that terrorist groups can end includingE

the group achieves it goals, it e#periences partial success, state repression destroys the group, the group

!urns out, the leadership is killed or imprisoned, there is a generational transition, the group loses popular

support, or new alternatives for the group emerge.[+%] While their arguments may e#plain why terrorism

ended today and not yesterday, the current study is concerned with understanding the underlying country<

level causes that e#tends a terrorist groupIs survival or facilitates its failure. "hus, we are interested in

assessing what factors aect the longevity of the terrorist organisationIs life span. "o accomplish this task,

we amass a large collection of groups from a more comprehensive dataset and estimate the factors that

relate to their years of survival. 's discussed a!ove, to our knowledge only a few studies attempt to use asimilar approachN these have focused, however, only on the transnational organisations found in ("B*'"B.

[+&] =y limiting their group analysis to only transnational attacks, they capture only part of the picture. (n

short, the divide !etween domestic and transnational terrorism may !e less important as interactions

!ecome more glo!al. (n order to !etter understand the life spans of all terrorist organisations, the data

source should include attacks !y organisations regardless of whether they only attack within one country or

whether they attack across national !orders. (n the ne#t section, we discuss how to dene and operationalie

terrorism, terrorist groups, and terror group survival.

De!ning "errorism# "error Groups# and Survival

Aening terrorism has !een an area of heated de!ate. 's Schmid and Congman noted, the 8search for an

adequate denition is still on,: yet 8consensus on an adequate social science denition of terrorismHis still

lacking, we areHsomewhat closer to solutions than we were some years ago.:[++] 'fter their careful

e#amination of over 1)) denitions, Schmid and Congman came up with a denition that included many

moving parts.[+] "his type of denition, or what 3unck and Oerkuilen call a ma(imalist denition, includes

too many elements, which could !e di9cult to empirically measure.[+-] 0urther, the denition potentiallyconfuses how these elements then relate to other concepts. 0or e#ample, over 1+P of the denitions that

Schmid and Congman survey include the innocence of victims as an important element of terrorism.[+5] "his

element would likely lead to the e#clusion of any attack on the military as a terrorist act, such as the

!om!ing of the 3arine !arracks in De!anon in 165% or the $))) attack on the $ 'ole. While we recognie

the importance of reducing the denition of terrorism to e#clude elements that o!fuscate the relationship

!etween terrorism and other concepts in the world >i.e., democracy, economic development, and


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counterterrorism, a minimalist denition is also pro!lematic. ' minimalist denition will have more

empirical referents, !ut will also fail to distinguish unlike events, such as terrorism and insurgency or

terrorism and genocide.[+6] =y incorporating into the denition an element that requires the target of the

violence to !e dierent from its intended audience, then terrorist events can !e separated from genocides

and insurgencies.[)] "his eort is especially important if we !elieve that these forms of con/ict have

dierent causal mechanisms.

*ecent research suggests using dierent operational denitions of terrorism to e#plore how sensitive

empirical inferences are to denitional specications.[1] "hus far, analyses that use various denitional

components of the @lo!al "errorism Aata!ase >@"A nd that the eects of key indicators on terrorism are

ro!ust to its dierent operational denitions.[$] "he @"A includes incidents that meet all of the following

three conditionsE

1. "he incident must be intentional Q the result of a conscious calculation on the part of aperpetrator.

$. "he incident must entail some level o$ violence or threat o$ violence < including propertyviolence, as well as violence against people.

%. "he perpetrators o$ the incidents must be sub%national actors& "his data!ase does notinclude acts of state terrorism.[%]

(n addition, the incidents must t at least $ of the following three criteriaE

'riterion () The a!t "ust be ai"ed at attaining a politi!al# e!ono"i!# religious# or so!ial goal. (n

terms of economic goals, the e#clusive pursuit of prot does not satisfy this criterion. (t must involve the

pursuit of more profound, systemic economic change.

'riterion *) There "ust be eviden!e of an intention to !oer!e# inti"idate# or !onvey so"e other

"essage to a larger audien!e $or audien!es% than the i""ediate vi!ti"s . (t is the act taken as a

totality that is considered, irrespective if every individual involved in carrying out the act was aware of this

intention. 's long as any of the planners or decision


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portion of the @"A. 0or this study we dene terrorism as the intentional threat or use of violence by sub

national actors for a political goal intended to convey a message to a larger audience than the victims of the

violence.[+] "his denition is consistent with the @"A, as 7riterion 1 suggests that terrorism is used to fulll

a political, religious, social, or economic goal. 7onsistent with Joman [], we chose to only add 8political:

to our denition as 8terrorismHis fundamentally and inherently politicalH[it] isHa!out powerE the pursuit of

power, the acquisition of power, and the use of power to achieve political change.: Bconomic interests,

religious !eliefs, or social change may motivate a group to act together, !ut their goals are inherently

coercive to change another individual or groupIs !ehaviour and are thus political. "he nal important portion

of our denition relates to dierentiating the audience of violence from the victim. (n other words, the

people who are killed are not the audience for the violence. "his audience is often a larger population, a

government, or some other third party. Aistinguishing !etween these groups helps dierentiate terrorism

from genocide >where the victim and audience are the same and other forms of political violence.

' terrorist organisation is then dened as a group that uses terrorism as descri!ed a!ove. While this

statement has face validity, it leads to some di9cult questions. 're all organisations that use terror, terrorist

groups? (f a group only uses one act of terror and uses nonviolent means in 66P of its other interactions,

should it !e la!eled a terrorist group? Since we are trying to identify why terrorist groups >and thus acts of

terror persist or decline, we need to la!el any group who uses this act as a terrorist group. When they stop

using this tactic, then they are no longer coded as a terrorist group. ;sing data on terrorist groups from the

@"A [-], we created a data!ase of terror organisations. =y using terrorist attacks as a way to esta!lish

which groups are terror groups, we avoid su!Mectively la!eling groups as terrorist and focus instead on their

actions. @roups that use terror thus are considered terrorist organisations. 's long as they use this act, the

group maintains this la!el. When the group desists, it no longer ts the criteria. "his is consistent with the

way scholars who study the reasons why groups deli!erately target civilians instead of using some other

strategy of resistance, think a!out the issue. (t is also consistent with the concerns of most governments

that face terror campaignsE they want to understand what makes terrorism end. (n sum, terrorist group

survival is conceptualied as the time !etween a groupIs rst attack and its last attack. Some operational

issues remain and will !e discussed in the *esearch Aesign section. We now turn to a discussion of the data

and research design.

Data

Terrorist +rganisations. "he @"A chronicles terrorist incidents across the glo!e from 16-) through $)1)

using media reports and other open sources.[5] When the source attri!utes an attack to a specic

perpetrator, the name is also recorded in the @"A. Fver half of the attacks in the @"A >+).%P were


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attri!uted to at least one specic perpetrator.[6] (n order to construct this dataset, we com!ined attacks

that were attri!uted to the same organisation to determine its 8start: date and its 8end: date. We recognie

that this measure of the organisationIs life span is only a pro#y !ecause organisations might have attacked

outside of our documented span without !eing attri!uted to the attack.[-)] Augan outlines other sources of

error when creating an organisational data!ase from the @"A or any other terrorist event data!ase that

relies on open sources.[-1] (n short, our measure of span represents the lower !ound estimate of the true

span. 0urthermore, these spans can also !e considered the !est measure of the organisationIs visi!le life

span. Since groups who use this form of violence are trying to change a policy, in/uence a pu!lic, or compel

a government, claiming credit or ensuring attri!ution of credit is necessary. (n fact, *apoport suggests that

this issue of taking credit for violent acts is one of the primary dierences !etween terror groups and

criminal organisations.[-$]

"he temporal domain of this study is 16-) to $)1). "he unit of analysis is the group


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found in the ("B*'"B data. 0urther, the num!er of incidents perpetrated !y these groups is considera!ly

larger, as they include !oth domestic and transnational attacks. 's Da0ree and Augan e#plain, a!out seven

out of every eight terror attacks are domestic in nature.[51]

=ecause the unit of analysis is the groupTop &og 3 2umber of %roups.

%roup 'apabilities. We also include measures that pro#y alternative e#planations of group survival from

previous research. "o control for and pro#y a groupIs capa!ilities, we use two varia!les that were measured

during the rst %+ days !eginning with the groupIs rst attack.[5%] 0irst, we created a dichotomous

measure of whether a group ever used multiple modalities of terrorism. "he measure is coded a 1 if the

group has ever done any com!ination of the followingE !om!ings, assassinations, hiMackings, kidnappings,

armed assaults, facility attacks, and hostage4ultiple4odality .[5&] @roups that

used only one tactic are marked as ero. We e#pect that groups that have more /e#i!ility to operate

dierently across attacks are likely to !e more capa!le and to survive longer. We created a second varia!le

that captures group capa!ilities that measures whether the group perpetrated attacks in more than one


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country >Transnational. "his dichotomous measure is coded as 1 if a group attacked in more than one

country during their rst year of operation and ero otherwise.[5+]

tate 'apabilities. =ecause the capa!ility of the state to control and even dismantle terrorist organisations

might in/uence the competitive environment and a groupIs capacity for survival, we include three measures

of state capa!ilities in the current analysis. 3easures of population and gross domestic product come from

the 4enn World "a!le [5], and geological terrain comes from research !y 0earon and Daitin. [5-] "hese

varia!les are measured during each year of the analysis, unless they are time invariant. We use a measure

of state capa!ility that is often used in studies of civil war onset and duration, @A4. (n terrorism research,

@A4 is generally used as a pro#y for the level of development in society > &evelopment .[55] @A4 is

measured in hundreds of thousands of dollars so that the odds ratio will !e easier to interpret. Since another

potential measure of state capa!ilities, the 7orrelates of War state material capa!ilities inde#, leads to an

increased num!er of missing o!servations, we e#clude it from our primary estimations. We discuss this

varia!le in greater detail in the appendi#. "he population of a state >5opulation might also in/uence its

capa!ilities and thus the survival of a terrorist group.[56] We include a logged measure of population from

the 4enn World "a!les.[6)] "he nal measure that pro#ies state capa!ilities is the percent mountainous

terrain in a country >4ountains.[61] (n civil war research, this is argued to increase the likelihood that re!els

can hide from the state and thus survive.

'ontrol 6ariables. Several control varia!les are also included in the analysis. 4olitical measures come from

the 4olity (O Aata 4roMect.[6$] Bthnic and religious measures come from research !y 0earon and Daitin.[6%]

[6&] (n the online appendi#, we list the specic varia!les and their original source. "o investigate the eects

democracy might have on a groupIs lifespan, we use a set of covariates related to regime characteristics and

institutions. We use the 4olity $ score as a measure of the level of democracy in a state. "he 4olity $ score

>&emocracy is created !y su!tracting the authoritarian score from a general democracy score that results in

a measure ranging from strongly authoritarian to R1) >strongly democratic. 's previous research

suggests [6+], dierent aspects of democracy might encourage or discourage terrorist group acts and

survival. Aemocracy has had an inconsistent eect on survival with some evidence that under specic

conditions it might encourage group longevity. We also control for the age of the current regime in power in

a given state > #ge of Regime. 0ully consolidated regimes may invite less violent contestation than regimes

that are new and have not esta!lished regularied means of political participation. Fn the other hand,

regimes that are older are more consolidated which suggests that dissidents who oppose the current order

are weak vis


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groups and how long they survive. "o control for this possi!ility we use a measure of the pro!a!ility that two

people randomly chosen from society will !e from dierent ethnic groups >1thnic 0ractionali7ation. ' similar

logic applies to religious heterogeneity. "o pro#y for this concept, we use a measure of the pro!a!ility that

two people randomly chosen from society will !e from dierent religious groups > Religious 0ractionali7ation.

[6] Some o!servers claim that certainly terrorism and possi!ly group survival might !e a function of

religious !elief, especially the desire to !uild a glo!al caliphate !y adherents of radical Sala (slam.[6-]

*eligion can !ind a group together and make the mem!ers see their struggle as a cosmic !attle !etween

good and evil.[65] We also use a measure of the percent of 3uslims >8 4uslim in society to pro#y the eect

that this might have on terrorist group survival.[66] Some might argue that the end of the 7old War ushered

a new era of con/ict.[1))] "o control for this, we include a dummy varia!le >'old War for whether groups

survived longer during the 7old War than in the period after this era.

We also include control varia!les for four of the ve maMor regions of the world, 1urope, #frica, #sia,

and #merica. "he reference region is the 3iddle Bast. 0inally, in order to model the time dependence, we

include three measures of num!er of years the group has !een in the data > /ife 9ears, /ife 9ears:, and /ife

9ears;. ' simple count of these years would assume a linear haard. ' squared version would assume a

quadratic relationship. (nclusion of the cu!ic term allows us to capture temporal dependence similar to

common parametric survival models as well as semi0ailt 1 β) R β1'omp1nvt R β$%r'apabilityt1


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*ecall that the unit of analysis is the groupTop &og 3 2umber of %roups=t . (f the +utbidding -ypothesis is

supported, we would e#pect the odds ratio for 2umber of %roupst to !e greater than oneN and if the Top &og

-ypothesis is supported, we e#pect the Top &ogt odds ratio to !e less than one in the model that e#cludes

the interaction. 0inally, if the (nteractive Jypothesis is supported, we e#pect the odds ratio of the interaction

two >Top &og 3 2umber of %roups=t to !e less than one.

"he ne#t set of control varia!les relate to the relationship !etween terrorist group survival >%r'apabilitytt'apabilityt in equation 1. "he group capa!ilities include 4ultiple

4odalityti.e., increasing the pro!a!ility of group failure. 7onversely, we e#pect the odds ratio of

mountains to !e less than one, increasing the chances of group survival.

'ontrolst include &emocracyt , #ge of Regimet , 1thnic 0ractionali7ationt , Religious 0ractionali7ationt , 5ercent

4uslimt , 'old Wart , 1urope, #frica, #sia, #merica, /ife 9ears, /ife 9ears:, and/ife 9ears;.

-esults

&escriptive tatistics. =efore addressing the hypotheses, we rst take a look at the data to get a !ettersense of how groups in the @"A have operated over time. We !egin !y e#amining the patterns of attack and

survival for the $,$$% terrorist organisations found in the @"A. 0igure 1 shows the num!er of terror attacks

>solid line in the world from 16-) to $)1) and the num!er of groups >dashed line who commit more than

half of these acts from the @"A. 3ost nota!le is that the two trends seem to track one another relatively

closely >r ).-5. "he deviation of these two lines shows that in the 16-)s, while there were many groups,

the overall num!er of attacks per known group was lower than in the 165)s, 6)s, or late $)))s >6 to 1 versus


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$) to 1. "his suggests that the num!er of attacks is not uniform across known groupsN and other factors

such as the economy, the level of democracy, or the international system may in/uence these levels.

7ontrary to conventional wisdom, the high point for !oth num!er of known groups and num!er of attacks

was the early 166)s >although attacks per group were not as high as in other periods.[1)&]

We see in this gure that the num!er of groups that attacked each year ranges from a low of &$ groups in

16-$ to a high of $%& groups in 166$. "his num!er drops again to another low in 1665 with only 5) groups

attacking. "he last decade in the series shows that the num!er of active groups ranges !etween 11) and

1-+. While the num!er of active groups never rises a!ove its 166$ peak, we know that there were a total of

$,$$% organisations that were attri!uted to attacks over this period. "his means that a large portion of the

groups were inactive during each year. (n fact, according to Augan [1)+] a maMority of the groups in the @"A

were only attri!uted to one attackN and a!out another $)P !ecame inactive within their rst year. Jowever,

the groups that were active for more than a year were also 8responsi!le: for more than 6%P of the attri!uted

attacks.[1)]

0igure


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might !e more likely to last longer than one year. (n order to get a !etter sense of the survival patterns of

these terrorist organisations, we estimate the !aseline survival rate with the Gaplan

include the group


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around T1-).6) to T&%,6-.+) >recall, that it is measured in values of T1))G. "he remaining summary

statistics show that all values are within reasona!le range.


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urvival 4odel Results. We now address the hypotheses with the odds ratios generated from the discrete

time survival models in "a!le $. 3odel 1 shows the ndings for the main eects for the +utbidding and Top

&og -ypotheses, while 3odel $ also includes an interaction !etween Top &og and 2umber of %roups for

the Interactive -ypothesis. "urning rst to the competitive environment we see that in !oth models the odds

ratio is a!ove one. (n 3odel 1, this can !e interpreted that with each additional competitor, the odds of

failing within the year increases !y ).)), holding all else constant. (n essence, we can think of this num!er

as the appro#imate increase in the pro!a!ility of failure that is attri!uted to an increase of one additional

competitor >or primary organisation. While at rst glance, this might seem like a small eect, the average

num!er of primary groups that use terrorism in a country year is 1). >see "a!le 1. "he -+th percentile for

this varia!le is 1+. "hat means that roughly $+P of all of the terrorist groups attack in a country in which 11

other groups are also attacking in a given year. (n this case, 1+ groups in one country during one year would

lead to an e#pected decrease in the survival time of any of the groups !y a!out 1$P. 't the most e#treme,

(taly in 16-5 had over -) groups, su!stantially decreasing the survival time for any one of those groups. "hus, the +utbidding -ypothesis is supported in these data.


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"urning now to the ndings for Top &og, we see that when a terrorist organisation is the most active in its

primary country during a given year, its pro!a!ility of failure is a!out ).& lower than the other primary

groups in that country. "his shows support for the Top &og -ypothesis. Ff course, this nding leads to the

question of whether "op Aog organisations do !etter or worse in a highly competitive environment, which is

the topic of the Interactive -ypothesis. "he results under 3odel $ show that the odds ratio of the Top &og 3

2umber of %roups interaction is less than one, supporting the hypothesis. "he Dikelihood *atio "est

comparing 3odels 1 and $ favors 3odel $ >p ).))), showing additional support for the Interactive

-ypothesis. While we cannot directly interpret the odds ratio for the interaction term !ecause it needs to !e

com!ined with the odds ratio for 2umber of %roups, we instead present in 0igure % the predicted pro!a!ility

of failure conditional on the num!er of competitors in a given year for "op Aog organisations and 2ot "op

Aog organisations.[11)] "his gure shows that when competition is low, each type of group has a pro!a!ility

of failing of around ).). Jowever, as competition increases, the pro!a!ility that a "op Aog organisation fails

drops dramatically, while that pro!a!ility increases for all other groups. (n a way, this is consistent with thestory that a hiker does not have to outrun a !ear during an attack, he or she only needs to outrun the person

they are with. (t is possi!le that when governments are !usy countering weaker terrorist organisations, the

stronger groups are !etter a!le to safely operate.

"his !rings us to the ndings for @roup 7apa!ility. We see !y the low odds ratios in !oth models that

organisations that were using multiple tactics andKor operating across national !orders during their rst year

are more likely to survive into the following year. (n fact, their chances of failing are a!out half that for other

organisations in the same county during the same year.


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0igure ;. 5robability that a %roup 0ails 'onditional on the 2umber of 'ompetitors

2+T1* #ll signicant covariates are set at mean, insignicant covariates are e(cluded.

"a!le $ also shows that controls that in/uence state capa!ilities from previous studies also impact survival.

(ncreases in &evelopment signicantly shorten the life span of terrorist organisations >or increase their risk of

failure. "he estimated odds ratio shows that a one unit change in &evelopment , which corresponds to an

increase of T1),))) in a countryIs per capita @A4, is e#pected to increase the risk that a group fails !y

roughly ).%P. We nd weak eects for 5opulation as it is only signicant in the model without the

interaction, and 4ountains is insignicant.

0inally, we see that #ge of Regime, 'old War , #frica, #merica and /ife 9ears all show signicant eects. 0irst,

every additional year that a regime has !een in place > #ge of the Regime leads to an average decrease in

the risk of a group ending !y around ).&P. "his num!er seems small, !ut the average age of a regime in thesample is nearly %+ years with a standard deviation of & years. ' one standard deviation increase in

the #ge of the Regime is e#pected to increase the survival of a group !y a!out 15P. Second, !eing involved

with the 'old War increases the pro!a!ility a group will fail !y more than half. "hird, the geographical

indicators show that groups operating in !oth 'sia and the 'mericas are more likely to fail !y the following

year than organisations in the 3iddle Bast. Similar to other approaches to modeling time dependence like

splines, we are not interested in the signicance of the life years varia!les. (nstead, we plotted the

pro!a!ility of failure conditional on the average values of the independent varia!les at dierent values for

the life years to e#amine their impact. Similar to previous work, the pro!a!ility of failure is high at the

!eginning and then su!sequently decreases until groups reach the age of appro#imately %) years old. 'fter

this point, the pro!a!ility of failure !egins to rise. =ecause only a few groups that make it to this age and

the recent endings of older groups, such as the 2ew 4eopleIs 'rmy in the 4hilippines or the (rish *epu!lican

'rmy, this rise is quite large.

'onclusions

's 7renshaw suggests, 8[s]ome processes of terrorism may !e independent of government action.:[111]Fur approach has !een to identify some of these processes in a cross


22/31

uses dierent kinds of attacks, targets multiple states, or uses the most costly forms of attack, the more

likely it will survive longer. While democracy has !een associated with the frequency of terrorism events, we

nd little support for the relationship !etween democracy and terrorist group survival.[11$] While

democracies may !e the target of more terrorism, groups facing these regimes are likely to last Must as long

as those facing autocratic regimes. Fne institutional characteristic, the age of the regime, does in/uence

group survival. Bven after controlling for these other known predictors of terrorism and terrorist group

survival, the out!idding hypothesis receives unqualied empirical support.

While our approach helps to !etter understand how certain states encourage or discourage terrorist group

survival !y evaluating conte#tual factors like the competitive environment, there are limitations to this

study. 0irst, we do not take into account the pro#imate factors that might lead to the end of a terrorist

group. "o the e#tent the pro#imate causes and conte#tual factors are independent of each other, our

ndings should !e un!iased from this omission. (nstead, investigations of how certain counterterror policies

increase or decrease group longevity or how certain organisational choices !y groups increase or decrease

their likelihood of survival should !e complementary to our ndings. 0urther, we investigated how general

repression aects group survival !ut not at a microlevel. While repression increased survival time, it did not

change any of the inferences from our other conte#tual varia!les. 'n analysis of these choices looking at

events and actions !y each group over a shorter temporal unit of aggregation such as daily, weekly or

monthly is necessary to model the dynamic interaction !etween terrorist group and states countering

terrorism. "his type of research will !e possi!le as more cross


23/31

[1] 7renshaw, 3artha. 1661. 8Jow "errorism Aeclines.: Terrorism and 5olitical 6iolence %>1E 6producing !acklash.

[1$] 7ronin. $)). 8Jow al$)) specically assesses why groups like 'l


24/31

[1&] =lom!erg, et al. $)1). 8Fn the Auration.:

[1+] =lom!erg et al. $)11. 8"errorist @roup Survival.:

[1] Cones and Di!icki. $))5. -ow Terrorism 1nds.

[1-] 0ortna, 4age. $)11. 8Ao "errorists Win? *e!elsI ;se of "errorism and 7ivil War Futcomes.: Working 4aper, 7olum!ia ;niversity, 2ew Vork.

[15] '!rahms, 3a#. 8Why "errorism Aoes 2ot Work.: International ecurity %1>$E &$1E 1


25/31

[%)] =loom $))+.

[%1] =loom $))+, 6+.

[%$] =lom!erg et al. $)11. 8"errorist @roup Survival.:

[%%] See *a!ushka, 'lvin and Genneth Shepsle. 16-$. 5olitics in 5lural ocieties* # Theory of &emocratic Instability . 7olum!us, FJE 3errill, and

Jorowit, Aonald D. 165+. 1thnic %roups in 'on!ict =erkeleyE ;niversity of 7alifornia 4ress.

[%&] Gaufman, Stuart. 166. 8Spiraling to Bthnic WarE Blites, 3asses, and 3oscow in 3oldovaIs 7ivil War.: International ecurity $1>$E 1)5<

1%5.

[%+] (!id.

[%] =ru!aker, *ogers, and Aavid Daitin. 1665. 8Bthnic and 2ationalist Oiolence.: #nnual Review of ociology $&E &$%


26/31

[&-] Bu!ank, William Deonard Wein!erg. 166&. 8Aoes Aemocracy Bncourage "errorism? Terrorism and 5olitical 6iolence >&E &1-Q&&%.

Bu!ank, William Deonard Wein!erg. 1665. 8"errorism and AemocracyE What *ecent Bvents Aisclose. Terrorism and 5olitical 6iolence 1)>1E

1)5Q115. Byerman, Coseph. 1665. 8"errorism and Aemocratic StatesE Soft "argets or 'ccessi!le Systems.: International Interactions $&>$E

1+1&E -+<

-55.

[&6] Bu!ank and Wein!erg.. 8Aoes Aemocracy Bncourage "errorism?:

[+)] Di. 8Aoes Aemocracy 4romote or *educe "ransnational "errorist (ncidents?:

[+1] "hey also have a much smaller sample of countries than what are availa!le from the @"A or ("B*'"B datasets. *and identies &5

groups and Cones and Di!icki >$))5 utilie a sample of $5 to perform descriptive analyses. "his is a classic case of selection !ias as they

only e#amine cases that failed thus selecting their cases !ased on the value of the dependent varia!le. "his likely !iases any inferences from

their study.

[+$] Cones and Di!icki. $))5. -ow Terrorism 1nds.

[+%] Cones and Di!icki. $))5. -ow Terrorism 1nds, p. $+6.

[+&] =lom!erg, et al. $)1). 8Fn the Auration.: and =lom!erg et al. $)11. 8"errorist @roup Survival.:

[++] 'le#, Schmid 4., and Congman C. 'l!ert. $))+. 5olitical Terrorism. 2ew =runswickE"ransaction 4u!lishers.

[+] "heir denition has over 1)) words and includes at least ten elements.

[+-] 3unck and Oerkuilen, $))$.

[+5] Schmid and Congman, $))5.

[+6] 3unck and Oerkuilen $))$, @oert $)).

[)] See Cenkins for a discussion of how terrorism is dierent from other forms of political violence, in part, !ecause of various audiences for

the violence. Cenkins, =rian 16-&. 8(nternational "errorismE ' 2ew Gind of Warfare.: *and 4u!lication, Santa =ar!ara.

[1] Voung, Coseph G., and 3ichael @. 0indley. $)11. 84romise and 4itfalls of "errorism *esearch.: International tudies Review 1%>%E &11


27/31

[$] Whether terrorism includes only domesticKhomegrown events, only foreignKtransnational events, or includingKe#cluding military does not

change the inferences drawn from several studies. See Voung and 0indley $)11 and Voung, Coseph G., and Daura Augan. $)11. 8Oeto 4layers

and "error.: Cournal of 5eace Research &5>1E 16


28/31

[--] Cones and Di!icki. $))5. -ow Terrorism 1nds.

[-5] 's mentioned a!ove, !ecause the ("B*'"B data only include data on transnational groups and attacks, they e#clude purely domestic

groups and acts. Whether these types of terrorism, domestic and transnational, have dierent etiologies is unclear >Bnders, Walter, Ghusrav

@ai!ulloev, and "odd Sandler. $)1). XAomestic Oersus

"ransnational "errorismE Aata, Aecomposition, and Aynamics.X 4aper 4resented at the "errorism and 4olicy 7onference, Aallas, "e#as. . =y

Must using transnational groups, however, the two types are !eing treated dierentlya priori.

[-6] =lom!erg, et al. $)1). 8Fn the Auration.:

[5)] Da0ree, @ary, Suep).))1. With an odds ratio of ).5, this nding suggests that for top dog groups only, each additional competitor decreases the

odds of failure !y a!out 1& percent. ' likelihood ratio test conrms that the interaction model is a !etter t >p).))1.

[5%] We cannot include measures of group sie or ideology as these measures e#ist for only a small portion of our groups. (n the future, we

plan to code these data. '!rahms does use a peak group sie measure for the mem!ers of his more limited sample of terrorist organisations,

which consists of +& groups that make the State AepartmentIs 0oreign "errorist Frganisation list. '!rahms, 3a#. $)1$. X"he 4olitical

Bectiveness of "errorism *evisited.X'omparative 5olitical tudies &+>%E %


29/31

[5] Jeston, 'lan, *o!ert Summers and =ettina 'ten, 5enn World Table Oersion .%, 7enter for (nternational 7omparisons of 4roduction,

(ncome and 4rices at the ;niversity of 4ennsylvania, 'ugust $))6.

[5-] 0earon, Cames A. and Aavid Daitin. $))%. 8Bthnicity, (nsurgency, and 7ivil War.: #merican 5olitical cience Review 6->1E -+$)11 also intepret @A4 as a pro#y for an attractive state target or as a

suita!le environment for skilled recruits >=enmelech and =erre!i $))-.

[56] =lom!erg et al. $)11. 8"errorist @roup Survival.:

[6)] Jeston, et al. $))6. 5enn World Table.

[61] "his measure comes from 0earon and Daitin >$))% and is a logged percentage of terrain in a country that is mountainous. (t is constant

over time.

[6$] 3arshall, 3onty @., and Geith Caggers. $)1). 5olity I6 &ata 5roKect* 5olitical Regime 'haracteristics and Transitions, $E %$6%E $$


30/31

[1)%] We coded all groups as eroes in $)1) as we could not conrm if they failed in that year or not. We also estimated the model without

this year and the results are su!stantively the same.

[1)&] "he compilers of the @"A caution users a!out comparing events from the 16-) through 166- period to those from the 1665 through

$))- period !ecause they were collected according to dierent methodologies. Since the latter data were collected prospectively, they may

systematically record fewer cases than the earlier data >httpEKKwww.start.umd.eduKgtdKusing


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E()*(+,(G SE+-,TY T)/-G) +/LL*0/*T,1E ESE*+)

5erspectives on Terrorism is a Mournal of the Terrorism Research

Initiative and the 'enter for Terrorism and ecurity tudies

I2 :;;L;LM B+nline=

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survival of the fittest why terrorist groups endure

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