Sample selection models, variants of which are the Heckman and Heckit models, are increasingly used by political scientists to accommodate data in which censoring of the dependent variable raises concerns of sample selectivity bias. Beyond demonstrating several pitfalls in the calculation of marginal effects and associated levels of statistical significance derived from these models, we argue that many of the empirical questions addressed by political scientists would – for both substantive and statistical reasons – be more appropriately addressed using an alternative but closely related procedure referred to as the two-part model (2PM). Aside from being simple to estimate, one key advantage of the 2PM is its less onerous identification requirements. Specifically, the model does not require the specification of so-called exclusion restrictions, variables that are included in the selection equation of the Heckit model but omitted from the outcome equation. Moreover, we argue that the interpretation of the marginal effects from the 2PM, which are in terms of actual outcomes, are more appropriate for the questions typically addressed by political scientists than the potential outcomes ascribed to the Heckit results. Drawing on data compiled by Sweeney (2003) from the Correlates of War database, we present an empirical analysis of conflict intensity illustrating that the choice between the sample selection model and 2PM can bear fundamentally on the conclusions drawn.
{"title":"Is Peace a Missing Value or a Zero?","authors":"Colin Vance, Nolan Ritter","doi":"10.2139/ssrn.2423259","DOIUrl":"https://doi.org/10.2139/ssrn.2423259","url":null,"abstract":"Sample selection models, variants of which are the Heckman and Heckit models, are increasingly used by political scientists to accommodate data in which censoring of the dependent variable raises concerns of sample selectivity bias. Beyond demonstrating several pitfalls in the calculation of marginal effects and associated levels of statistical significance derived from these models, we argue that many of the empirical questions addressed by political scientists would – for both substantive and statistical reasons – be more appropriately addressed using an alternative but closely related procedure referred to as the two-part model (2PM). Aside from being simple to estimate, one key advantage of the 2PM is its less onerous identification requirements. Specifically, the model does not require the specification of so-called exclusion restrictions, variables that are included in the selection equation of the Heckit model but omitted from the outcome equation. Moreover, we argue that the interpretation of the marginal effects from the 2PM, which are in terms of actual outcomes, are more appropriate for the questions typically addressed by political scientists than the potential outcomes ascribed to the Heckit results. Drawing on data compiled by Sweeney (2003) from the Correlates of War database, we present an empirical analysis of conflict intensity illustrating that the choice between the sample selection model and 2PM can bear fundamentally on the conclusions drawn.","PeriodicalId":234067,"journal":{"name":"Conflict Studies: Scientific Study eJournal","volume":"144 ","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120873284","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Spanish Abstract: La teoria de juegos desdibuja las estrategias considerando la situacion de los actores. La presente investigacion expone la aplicacion de la teoria de juegos al periodo belico de Guatemala. El acercamiento de la teoria de juegos desde la vision del conflicto se complementa con la utilizacion del metodo historico para analizar las estrategias de los actores: La guerrilla y el ejercito.English Abstract: Game theory is aims to understand the strategy of two or more players based on their actions. The present investigation applies game theory to the belic period in Guatemala. The approach of game theory adapted with the historic method is used to explained the strategies of two main actors in the periods of 1960 to 1970 in Guatemala: the army and the guerrilla.
{"title":"Teoría De Juegos Aplicada Al Conflicto Bélico De Guatemala: Período 1960-1970 (Game Theory Applied to the Belic Conflict of Guatemala: Period 1960-1970)","authors":"M. Garita","doi":"10.2139/SSRN.2555679","DOIUrl":"https://doi.org/10.2139/SSRN.2555679","url":null,"abstract":"Spanish Abstract: La teoria de juegos desdibuja las estrategias considerando la situacion de los actores. La presente investigacion expone la aplicacion de la teoria de juegos al periodo belico de Guatemala. El acercamiento de la teoria de juegos desde la vision del conflicto se complementa con la utilizacion del metodo historico para analizar las estrategias de los actores: La guerrilla y el ejercito.English Abstract: Game theory is aims to understand the strategy of two or more players based on their actions. The present investigation applies game theory to the belic period in Guatemala. The approach of game theory adapted with the historic method is used to explained the strategies of two main actors in the periods of 1960 to 1970 in Guatemala: the army and the guerrilla.","PeriodicalId":234067,"journal":{"name":"Conflict Studies: Scientific Study eJournal","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122809998","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Research on the future of policing generally ignores the problem of police violence. The author articulates a series of important structural level factors predicted to influence situational variables connected to the type, amount, and severity of police violence in the future. Relationships among the variables are posited, then assembled into a tentative causal model. The author concludes by discussing alternative methodologies for testing propositions from this model.
{"title":"The Future of Municipal Police Violence in Advanced Industrialized Democracies: Towards a Structural Causal Model","authors":"Jeffrey Ian Ross","doi":"10.2139/ssrn.2436017","DOIUrl":"https://doi.org/10.2139/ssrn.2436017","url":null,"abstract":"Research on the future of policing generally ignores the problem of police violence. The author articulates a series of important structural level factors predicted to influence situational variables connected to the type, amount, and severity of police violence in the future. Relationships among the variables are posited, then assembled into a tentative causal model. The author concludes by discussing alternative methodologies for testing propositions from this model.","PeriodicalId":234067,"journal":{"name":"Conflict Studies: Scientific Study eJournal","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114713945","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Thanks to sustained economic growth and key investments in military capabilities, India will face growing demands from within and the international community to seek and play a greater role in global security affairs. The values and interests likely to guide India’s future behavior will be a mixture of old and new, eastern and western. India’s international aspirations have an important pre-history, covered in this chapter’s first section where non-alignment, as idea and practice, is explored for its enduring significance. India’s relevance as a security actor is assessed in terms of its activities and capacity to influence developments within two security zones of major contemporary importance: Afghanistan and the Indian Ocean. Finally, a section on the constraints and challenges examines India’s ability to navigate a multi-polar world, the fallout and gains of nuclearization, the 2008 Indo-US nuclear deal, as well as ‘the weaknesses from within’ in terms of human security.
{"title":"India as Global Security Actor","authors":"Jivanta Schōttli, Markus Pauli","doi":"10.2139/ssrn.3575803","DOIUrl":"https://doi.org/10.2139/ssrn.3575803","url":null,"abstract":"Thanks to sustained economic growth and key investments in military capabilities, India will face growing demands from within and the international community to seek and play a greater role in global security affairs. The values and interests likely to guide India’s future behavior will be a mixture of old and new, eastern and western. India’s international aspirations have an important pre-history, covered in this chapter’s first section where non-alignment, as idea and practice, is explored for its enduring significance. India’s relevance as a security actor is assessed in terms of its activities and capacity to influence developments within two security zones of major contemporary importance: Afghanistan and the Indian Ocean. Finally, a section on the constraints and challenges examines India’s ability to navigate a multi-polar world, the fallout and gains of nuclearization, the 2008 Indo-US nuclear deal, as well as ‘the weaknesses from within’ in terms of human security.","PeriodicalId":234067,"journal":{"name":"Conflict Studies: Scientific Study eJournal","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131746755","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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