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Collective Action in Networks: Evidence from the Chilean Student Movement

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  • Felipe González

Abstract

Hundreds of thousands of students skipped school during the 2011 student movement in Chile to protest and reform educational institutions. Using administrative data on millions of students’ daily school attendance on protest days, this paper presents robust evidence of school absenteeism following a threshold model of collective behavior. Students skipped school on a protest day only when more than 40% of the members of their networks also skipped school.

Suggested Citation

  • Felipe González, 2018. "Collective Action in Networks: Evidence from the Chilean Student Movement," Documentos de Trabajo 509, Instituto de Economia. Pontificia Universidad Católica de Chile..
    • Handle: RePEc:ioe:doctra:509
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    as
    1. Marco Manacorda & Andrea Tesei, 2020. "Liberation Technology: Mobile Phones and Political Mobilization in Africa," Econometrica, Econometric Society, vol. 88(2), pages 533-567, March.
    2. Lohmann, Susanne, 1993. "A Signaling Model of Informative and Manipulative Political Action," American Political Science Review, Cambridge University Press, vol. 87(2), pages 319-333, June.
    3. Joseph G. Altonji & Todd E. Elder & Christopher R. Taber, 2005. "Selection on Observed and Unobserved Variables: Assessing the Effectiveness of Catholic Schools," Journal of Political Economy, University of Chicago Press, vol. 113(1), pages 151-184, February.
    4. Anselm Hager & Lukas Hensel & Johannes Hermle & Christopher Roth, 2019. "Strategic Interdependence in Political Movements and Countermovements," CESifo Working Paper Series 7790, CESifo.
    5. Anselm Hager & Lukas Hensel & Johannes Hermle & Christopher Roth, 2023. "Political Activists as Free Riders: Evidence from a Natural Field Experiment," The Economic Journal, Royal Economic Society, vol. 133(653), pages 2068-2084.
    6. Bramoullé, Yann & Djebbari, Habiba & Fortin, Bernard, 2009. "Identification of peer effects through social networks," Journal of Econometrics, Elsevier, vol. 150(1), pages 41-55, May.
    7. Alberto Abadie & Joshua Angrist & Guido Imbens, 2002. "Instrumental Variables Estimates of the Effect of Subsidized Training on the Quantiles of Trainee Earnings," Econometrica, Econometric Society, vol. 70(1), pages 91-117, January.
    8. Gordon Tullock, 1971. "The paradox of revolution," Public Choice, Springer, vol. 11(1), pages 89-99, September.
    9. Gordon B. Dahl & Katrine V. L?ken & Magne Mogstad, 2014. "Peer Effects in Program Participation," American Economic Review, American Economic Association, vol. 104(7), pages 2049-2074, July.
    10. Coralio Ballester & Antoni Calvó-Armengol & Yves Zenou, 2006. "Who's Who in Networks. Wanted: The Key Player," Econometrica, Econometric Society, vol. 74(5), pages 1403-1417, September.
    11. Haiqing Xu, 2018. "Social Interactions In Large Networks: A Game Theoretic Approach," International Economic Review, Department of Economics, University of Pennsylvania and Osaka University Institute of Social and Economic Research Association, vol. 59(1), pages 257-284, February.
    12. Tomás Rau, 2013. "Modeling structural equations with endogenous regressors and heterogeneity through derivative constraints," Quantitative Economics, Econometric Society, vol. 4(1), pages 125-148, March.
    13. Kuran, Timur, 1991. "The East European Revolution of 1989: Is It Surprising That We Were Surprised?," American Economic Review, American Economic Association, vol. 81(2), pages 121-125, May.
    14. V. Joseph Hotz & Robert A. Miller, 1993. "Conditional Choice Probabilities and the Estimation of Dynamic Models," The Review of Economic Studies, Review of Economic Studies Ltd, vol. 60(3), pages 497-529.
    15. Jennifer M. Larson & Jonathan Nagler & Jonathan Ronen & Joshua A. Tucker, 2019. "Social Networks and Protest Participation: Evidence from 130 Million Twitter Users," American Journal of Political Science, John Wiley & Sons, vol. 63(3), pages 690-705, July.
    16. Duncan Sheppard Gilchrist & Emily Glassberg Sands, 2016. "Something to Talk About: Social Spillovers in Movie Consumption," Journal of Political Economy, University of Chicago Press, vol. 124(5), pages 1339-1382.
    17. David Card & Alexandre Mas & Jesse Rothstein, 2008. "Tipping and the Dynamics of Segregation," The Quarterly Journal of Economics, President and Fellows of Harvard College, vol. 123(1), pages 177-218.
    18. William A. Brock & Steven N. Durlauf, 2001. "Discrete Choice with Social Interactions," The Review of Economic Studies, Review of Economic Studies Ltd, vol. 68(2), pages 235-260.
    19. Kline Patrick & Santos Andres, 2012. "A Score Based Approach to Wild Bootstrap Inference," Journal of Econometric Methods, De Gruyter, vol. 1(1), pages 23-41, August.
    20. Toke S. Aidt & Raphaël Franck, 2015. "Democratization Under the Threat of Revolution: Evidence From the Great Reform Act of 1832," Econometrica, Econometric Society, vol. 83, pages 505-547, March.
    21. Dur, Robert & Sol, Joeri, 2010. "Social interaction, co-worker altruism, and incentives," Games and Economic Behavior, Elsevier, vol. 69(2), pages 293-301, July.
    22. Honoré,Bo & Pakes,Ariel & Piazzesi,Monika & Samuelson,Larry (ed.), 2017. "Advances in Economics and Econometrics," Cambridge Books, Cambridge University Press, number 9781316510520.
    23. Barbera, Salvador & Jackson, Matthew O., 2020. "A Model of Protests, Revolution, and Information," Quarterly Journal of Political Science, now publishers, vol. 15(3), pages 297-335, July.
    24. Emily Oster, 2019. "Unobservable Selection and Coefficient Stability: Theory and Evidence," Journal of Business & Economic Statistics, Taylor & Francis Journals, vol. 37(2), pages 187-204, April.
    25. Alexander Coppock & Donald P. Green, 2016. "Is Voting Habit Forming? New Evidence from Experiments and Regression Discontinuities," American Journal of Political Science, John Wiley & Sons, vol. 60(4), pages 1044-1062, October.
    26. Giacomo De Giorgi & Michele Pellizzari & Silvia Redaelli, 2010. "Identification of Social Interactions through Partially Overlapping Peer Groups," American Economic Journal: Applied Economics, American Economic Association, vol. 2(2), pages 241-275, April.
    27. David Yanagizawa-Drott, 2014. "Propaganda and Conflict: Evidence from the Rwandan Genocide," The Quarterly Journal of Economics, President and Fellows of Harvard College, vol. 129(4), pages 1947-1994.
    28. Marco Manacorda, 2012. "The Cost of Grade Retention," The Review of Economics and Statistics, MIT Press, vol. 94(2), pages 596-606, May.
    29. Francesco Passarelli & Guido Tabellini, 2017. "Emotions and Political Unrest," Journal of Political Economy, University of Chicago Press, vol. 125(3), pages 903-946.
    30. Michael Suk-Young Chwe, 2000. "Communication and Coordination in Social Networks," The Review of Economic Studies, Review of Economic Studies Ltd, vol. 67(1), pages 1-16.
    31. Christopher Blattman & Edward Miguel, 2010. "Civil War," Journal of Economic Literature, American Economic Association, vol. 48(1), pages 3-57, March.
    32. Halberstam, Yosh & Knight, Brian, 2016. "Homophily, group size, and the diffusion of political information in social networks: Evidence from Twitter," Journal of Public Economics, Elsevier, vol. 143(C), pages 73-88.
    33. Andreas Madestam & Daniel Shoag & Stan Veuger & David Yanagizawa-Drott, 2013. "Do Political Protests Matter? Evidence from the Tea Party Movement," The Quarterly Journal of Economics, President and Fellows of Harvard College, vol. 128(4), pages 1633-1685.
    34. Blume, Lawrence E. & Brock, William A. & Durlauf, Steven N. & Ioannides, Yannis M., 2010. "Identification of Social Interactions," Economics Series 260, Institute for Advanced Studies.
    35. Bryan S. Graham, 2015. "Methods of Identification in Social Networks," Annual Review of Economics, Annual Reviews, vol. 7(1), pages 465-485, August.
    36. David Roodman & James G. MacKinnon & Morten Ørregaard Nielsen & Matthew D. Webb, 2019. "Fast and wild: Bootstrap inference in Stata using boottest," Stata Journal, StataCorp LP, vol. 19(1), pages 4-60, March.
    37. Honoré,Bo & Pakes,Ariel & Piazzesi,Monika & Samuelson,Larry (ed.), 2017. "Advances in Economics and Econometrics," Cambridge Books, Cambridge University Press, number 9781108400022.
    38. repec:cup:apsrev:v:113:y:2019:i:04:p:1012-1028_00 is not listed on IDEAS
    39. Matthew O. Jackson, 2019. "The Friendship Paradox and Systematic Biases in Perceptions and Social Norms," Journal of Political Economy, University of Chicago Press, vol. 127(2), pages 777-818.
    40. Bei Qin & David Strömberg & Yanhui Wu, 2017. "Why Does China Allow Freer Social Media? Protests versus Surveillance and Propaganda," Journal of Economic Perspectives, American Economic Association, vol. 31(1), pages 117-140, Winter.
    41. Whitney K. Newey & James L. Powell & Francis Vella, 1999. "Nonparametric Estimation of Triangular Simultaneous Equations Models," Econometrica, Econometric Society, vol. 67(3), pages 565-604, May.
    42. Davide Cantoni & David Y Yang & Noam Yuchtman & Y Jane Zhang, 2019. "Protests as Strategic Games: Experimental Evidence from Hong Kong's Antiauthoritarian Movement," The Quarterly Journal of Economics, President and Fellows of Harvard College, vol. 134(2), pages 1021-1077.
    43. Angrist, Joshua D., 2014. "The perils of peer effects," Labour Economics, Elsevier, vol. 30(C), pages 98-108.
    44. Steven N. Durlauf & Yannis M. Ioannides, 2010. "Social Interactions," Annual Review of Economics, Annual Reviews, vol. 2(1), pages 451-478, September.
    45. Honoré,Bo & Pakes,Ariel & Piazzesi,Monika & Samuelson,Larry (ed.), 2017. "Advances in Economics and Econometrics," Cambridge Books, Cambridge University Press, number 9781108400008.
    46. Timur Kuran, 1989. "Sparks and prairie fires: A theory of unanticipated political revolution," Public Choice, Springer, vol. 61(1), pages 41-74, April.
    47. Charles F. Manski, 1993. "Identification of Endogenous Social Effects: The Reflection Problem," The Review of Economic Studies, Review of Economic Studies Ltd, vol. 60(3), pages 531-542.
    48. Chris Edmond, 2013. "Information Manipulation, Coordination, and Regime Change," The Review of Economic Studies, Review of Economic Studies Ltd, vol. 80(4), pages 1422-1458.
    49. Jonathan Guryan & Kory Kroft & Matthew J. Notowidigdo, 2009. "Peer Effects in the Workplace: Evidence from Random Groupings in Professional Golf Tournaments," American Economic Journal: Applied Economics, American Economic Association, vol. 1(4), pages 34-68, October.
    50. Yuyu Chen & David Y. Yang, 2019. "The Impact of Media Censorship: 1984 or Brave New World?," American Economic Review, American Economic Association, vol. 109(6), pages 2294-2332, June.
    51. Áureo de Paula, 2013. "Econometric Analysis of Games with Multiple Equilibria," Annual Review of Economics, Annual Reviews, vol. 5(1), pages 107-131, May.
    52. Honoré,Bo & Pakes,Ariel & Piazzesi,Monika & Samuelson,Larry (ed.), 2017. "Advances in Economics and Econometrics," Cambridge Books, Cambridge University Press, number 9781108414982.
    53. Hsieh, Chang-Tai & Urquiola, Miguel, 2006. "The effects of generalized school choice on achievement and stratification: Evidence from Chile's voucher program," Journal of Public Economics, Elsevier, vol. 90(8-9), pages 1477-1503, September.
    54. Ruben Enikolopov & Alexey Makarin & Maria Petrova, 2020. "Social Media and Protest Participation: Evidence From Russia," Econometrica, Econometric Society, vol. 88(4), pages 1479-1514, July.
    55. Elster, Jon, 1989. "Social Norms and Economic Theory," Journal of Economic Perspectives, American Economic Association, vol. 3(4), pages 99-117, Fall.
    56. Thomas Fujiwara & Kyle Meng & Tom Vogl, 2016. "Habit Formation in Voting: Evidence from Rainy Elections," American Economic Journal: Applied Economics, American Economic Association, vol. 8(4), pages 160-188, October.
    57. William A. Brock & Steven N. Durlauf, 2010. "Adoption Curves and Social Interactions," Journal of the European Economic Association, MIT Press, vol. 8(1), pages 232-251, March.
    58. Enos, Ryan D. & Kaufman, Aaron R. & Sands, Melissa L., 2019. "Can Violent Protest Change Local Policy Support? Evidence from the Aftermath of the 1992 Los Angeles Riot," American Political Science Review, Cambridge University Press, vol. 113(4), pages 1012-1028, November.
    59. Bet Caeyers & Marcel Fafchamps, 2016. "Exclusion Bias in the Estimation of Peer Effects," NBER Working Papers 22565, National Bureau of Economic Research, Inc.
    60. Ricardo Perez-Truglia & Guillermo Cruces, 2017. "Partisan Interactions: Evidence from a Field Experiment in the United States," Journal of Political Economy, University of Chicago Press, vol. 125(4), pages 1208-1243.
    61. Whitney K. Newey & James L. Powell, 2003. "Instrumental Variable Estimation of Nonparametric Models," Econometrica, Econometric Society, vol. 71(5), pages 1565-1578, September.
    62. Yitzhaki, Shlomo, 1996. "On Using Linear Regressions in Welfare Economics," Journal of Business & Economic Statistics, American Statistical Association, vol. 14(4), pages 478-486, October.
    63. De Mesquita, Ethan Bueno, 2010. "Regime Change and Revolutionary Entrepreneurs," American Political Science Review, Cambridge University Press, vol. 104(3), pages 446-466, August.
    64. Joel L. Horowitz, 2011. "Applied Nonparametric Instrumental Variables Estimation," Econometrica, Econometric Society, vol. 79(2), pages 347-394, March.
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    Cited by:

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    8. Alejandra Agustina Martínez, 2023. "Raise your voice! Activism and peer effects in online social networks," Discussion Papers 2023-05, Nottingham Interdisciplinary Centre for Economic and Political Research (NICEP).
    9. Juan S. Morales, Margaret Samahita, 2023. "Can Social Pressure Stifle Free Speech," LCERPA Working Papers bm0140, Laurier Centre for Economic Research and Policy Analysis.
    10. Anselm Hager & Lukas Hensel & Johannes Hermle & Christopher Roth, 2019. "Strategic Interdependence in Political Movements and Countermovements," CESifo Working Paper Series 7790, CESifo.
    11. Janus, Thorsten, 2023. "Short and long run democracy diffusion," European Journal of Political Economy, Elsevier, vol. 78(C).
    12. Pablo A. Celhay & Emilio Depetris-Chauvin & Cristina Riquelme, 2023. "When a Strike Strikes Twice: Massive Student Mobilizations and Teenage Pregnancy in Chile," Working Papers 267, Red Nacional de Investigadores en Economía (RedNIE).
    13. Boris Ginzburg & José-Alberto Guerra, 2021. "Guns, pets, and strikes: an experiment on identity and political action," Documentos CEDE 19932, Universidad de los Andes, Facultad de Economía, CEDE.
    14. Jarke-Neuert, Johannes & Perino, Grischa & Schwickert, Henrike, 2021. "Free-Riding for Future: Field Experimental Evidence of Strategic Substitutability in Climate Protest," SocArXiv sh6dm, Center for Open Science.
    15. Pablo Celhay & Emilio Depetris-Chauvin & María Cristina Riquelme, 2020. "When a Strike Streikes Twice: Massive Student Mobilizations and Teenage," Documentos de Trabajo 550, Instituto de Economia. Pontificia Universidad Católica de Chile..
    16. Zhou, Yonghong, 2023. "Influence of political movement on fields of study: Evidence from Hong Kong," European Journal of Political Economy, Elsevier, vol. 79(C).
    17. Felipe González & Esperanza Johnson, 2018. "Políticas de inclusión universitaria y comportamiento estratégico en educación secundaria," Estudios Públicos, Centro de Estudios Públicos, vol. 0(149), pages 41-73.
    18. Gisli Gylfason, 2023. "From Tweets to the Streets: Twitter and Extremist Protests in the United States," PSE Working Papers halshs-04188189, HAL.
    19. Niklas Potrafke & Felix Roesel, 2022. "Online Versus Offline: Which Networks Spur Protests?," CESifo Working Paper Series 9969, CESifo.
    20. Camilo García-Jimeno & Angel Iglesias & Pinar Yildirim, 2022. "Information Networks and Collective Action: Evidence from the Women's Temperance Crusade," American Economic Review, American Economic Association, vol. 112(1), pages 41-80, January.
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