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each event contained in Mickolus’ (1980) Transnational Terrorism: A Chronology of Events,
1968-1979 and checked them against accounts in The New York Times and the London Times.
Operationally, terrorists claim responsibility for acts of terror when they publicly state, through a
spokesperson or in writing (e.g., letters sent to reporters, pamphlets left at the scene of the
attack), the name of their group and their culpability for the attack. Reports by government
officials that identify those responsible are not considered to be claims of responsibility. I also
did not count the use of code words by those issuing threats unless there was evidence that the
group using the code word to authenticate their threat also identified themselves to authorities.
Although the use of code words is more common in the Northern Ireland conflict than in the
Israeli-Palestinian dispute, knowledge of the code word did not always help members of the
government identify those responsible for acts of violence. For this reason, use of code words is
not tantamount to taking responsibility for terror.
The strength of this approach is that it produces cross-checked, and therefore relatively
accurate, data on claims of responsibility. The weakness of this approach is that it potentially
undercounts the number of claims of responsibility made by terrorist groups. Because Mickolus’
Chronology provides the basic source material on each event and identifying claims of
responsibility was not a principle concern of his, it is possible that the some claimed events went
overlooked. It is unlikely, however, that any undercounting might bias the results because there
is no more reason to believe that Mickolus systematically failed to identify claims of
responsibility in his case descriptions (see Mickolus, 1980).
Independent Variables
Competition: The most direct measure of situational competitiveness is the number of groups
Convention