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Ronit Nirel and Malka Gorfine

Applied Statistics Laboratory
Department of Statistics
The Hebrew University of Jerusalem

April 2000


The Intergroup Prisoner's Dilemma (IPD) game was suggested by Bornstein (1992) for modeling intergroup conflicts over continuous public goods. We analyze data of an experiment in which the IPD game was played for 150 rounds, under three matching conditions. The objective is to study differences in the investment patterns of players in the different groups. A repeated measures analysis (Goren and Bornstein, 1999) involved data aggregation and strong distributional assumptions. Here we introduce a non-parametric approach based on permutation tests, applied to the raw data. Two new measures, the cumulative investment and the normalized cumulative investment, provide additional insight into the differences between groups. The proposed tests, based on the area under the investment curves, identify overall and pairwise differences between groups. A simultaneous confidence band for the mean difference curve is used to detect games which account for pairwise differences.

Key words: Randomization tests; Multiple comparisons; Displacement approach; Conflict resolution problems.

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Last modified: 28/02/01