Riemersma, R.A.

Smies, M.

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The non-concept of ’war-proneness’: Naar aanleiding van H. W. Houweling and J. G. Siccama, War in the foreign policies of nations, Acta Politica, 1981 nr. 1, 67-99

Leiden University Scholary Publications

The non-concept of ’war-proneness’: Naar aanleiding van H. W. Houweling and J. G. Siccama,War in the foreign policies of nations, Acta Politica, 1981 nr. 1, 67-99Smies, M.; Riemersma, R.A.CitationSmies, M., & Riemersma, R. A. (1981). The non-concept of ’war-proneness’: Naar aanleiding van H. W. Houweling and J. G.Siccama, War in the foreign policies of nations, Acta Politica, 1981 nr. 1, 67-99. Acta Politica, 16: 1981(4), 531-533. Retrievedfrom https://hdl.handle.net/1887/3452191 Version: Publisher's VersionLicense: Leiden University Non-exclusive licenseDownloadedfrom: https://hdl.handle.net/1887/3452191 Note: To cite this publication please use the final published version (if applicable).AP 81/4DiscussieThe non-concept of ’war-proneness’by Maarten Smies and Riemke A. RiemersmaRecently, Houweling and Siccama^ used some thirty pages of this journal to introduce the concept of ’war-proneness’ to explain why some countries are engaged more in wars than others. We contend that war-proneness as used by the authors is a non-concept and that it is fruitless to pursue this line of research.Houweling and Siccama fitted a Poisson distribution to three data sets on war engagement by a number of nations. Since this distribution did not give a satisfactory fit, they concluded that individual nations are not equally probable to be engaged in war. They also stated assumptions of differential probability of war participation between groups of nations, leading to a negative binomial distribution (nbd) of war engagement over countries. This distribution was found to fit satisfactorily two of the data sets. Because other assumptions of war participation probability among nations may also give rise to statistical distributions fitting the data sets, they call for such assumptions to be put forward. This they assert, ’is a suitable way to explore the unknown territory of causation of national war participations. A comparison of the predicted outcomes with the observed ones may steer research in fruitful directions’.’^Here we take issue with Houweling and Siccama, as we cannot see how postulating assumptions that give rise to a statistical distribution fitting the data sets, may give any insight into the causes of war participation. To explain our stance we rely upon references in the field of theoretical ecology, where the problem in a different guise is a familiar one. More specifically we shall draw from the standard text by Pielou®, one of Houweling and Siccama’s own references.^The basic problem is to find the true distribution of X, the mean number of war engagements per nation, because the concept of war-proneness requires that such a distribution exists. That is, if we would know how likely nations are to become engaged in war, then we would be able to define X’s probability density function. However, this in general we do not know. Therefore, Houweling and Siccama have set out to find a theoretical statistical distribu­tion, of which their data sets can in fact be shown to be samples. That they have chosen a Pearson type III distribution is not surprising, because, as531AP 81/4Pielou points out: . whatever X’s true distribution it is likely that some type III curve can be found to approximate it closely. A true type III variate may have any nonnegative value and the curve may be unimodal or J-shaped’.® In other words: a Pearson type III distribution fits (almost) any data and its explanatory power is therefore very limited. To expand our argument: since the nbd is a compound Poisson, we are free to define the component Poisson distributions in whichever way we like. Houweling and Siccama postulated different groups of nations to have different, but within groups constant chances of war participation. Had they postulated that all nations had an equal, but in different time periods different probability of war engagement, the same nbd would have followed and the same fit to the data sets would have been obtained. Thus, we are not able to choose between all different compound Poisson distributions imaginable, let alone to decide into which ’fruitful directions’ to steer our research into the underlying causes. Besides, rather than derive the nbd as a compound Poisson, we may obtain it as a generalized Poisson distribution.® In war-proneness terminology this amounts to assuming that there are groups of nations with a certain war engagement probability, but that the number of nations per group is a random variate. (In the compound Poisson it is the war engagement expectancy which is the random variate). In this case the same fit to the data sets would also obtain, opening up an even wider field of research.To add to the richness of research possibilities, there are several more statistical distributions, that are likely to give a good enough fit to the data sets. We mention the logarithmic and geometric series and the Poisson log­normal distributions.’ If one or more of those would fit the data sets at or below the chosen level of probability, more sets of war-proneness assumptions could be worked out for further scrutiny. However, ’while specific... as­sumptions imply a unique statistical distribution, the converse is not true; a variety of different circumstances can imply the same distribution’.® There­fore, contrary to what Houweling and Siccama’s paper purports®, war-pro- neness analysis does not effectively restrict the scope of research into war causation.We conclude that war-proneness as a statistical concept is irrelevant for the study of war causation. If one consults Pielou to extract the formulae of the nbd’“, one can hardly fail to notice her statement in the next paragraph that ’it is futile to try to reach conclusions about the mechanism underlying a particular observed pattern simply by examining the observed distribution of the number of individuals per unit’.” Although Houweling and Siccama have indicated that they themselves are aware of this’^, they appear to have failed to grasp its full implication, namely that their approach cannot yield worth­while results.’®M. Smies and R. A. Riemersma The non-concept of ’war-proneness’Notes1. Houweling, H. W. and Siccama, J. G. (1981), ’War in the Foreign Policies of Nations: An Analysis of War-Proneness’, In: Acta Politica, Vol. 16, pp. 67-99.2. Op. cit., p. 76.3. Pielou, E. C. (1969), An Introduction to Mathematical Ecology, New York: Wiley. We used the revised edition Pielou, E. C. (1977), Mathematical Ecology, New York: Wiley, but checked for possible discrepancies with the first edition and found none as regards the current subject matter.4. Houweling and Siccama (1981), op. cit., note 21, p. 85.5. Pielou (1969), op. cit., p. 87.6. Pielou (1969), op. cit., pp. 83 ff.7. Pielou (1977), op. cit.. Ch. 18. May, R. M. (1975), ’Patterns of Species Abun­dance and Diversity’, In: Cody, M. L. and Diamond, J. M. (Eds.), Ecology and Evolution of Communities, Cambridge (Mass.): Harvard University Press, pp. 81- 120. Engen, S. (1979), ’Stochastic Abundance Models in Ecology’, In: Biometrics, Vol. 32, pp. 331-338.8. May (1975), op. cit., p. 88.9. Houweling and Siccama (1981), op. cit.. Section 4, pp. 83-84.10. Pielou (1969), op. cit., p. 87. We observe that Houweling and Siccama (1981), op. cit., p. 77 in their derivation of the nbd use the exact wording by Pielou, although no note to this effect is given. See also their note 21, p. 85.11. Pielou (1969), op. cit., p. 88.12. Houweling and Siccama (1981), op. cit., p. 81, line 11; p. 84, lines 11-13.13. Houweling and Siccama (1981), op. cit., p. 83, lines 15-17; p. 84, lines 18-19.

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The non-concept of ’war-proneness’: Naar aanleiding van H. W. Houweling and J. G. Siccama, War in the foreign policies of nations, Acta Politica, 1981 nr. 1, 67-99

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