I & K Social Net

NEP: New Economics Papers
Social Norms and Social Capital

Edited by:	Fabio Sabatini
	University of Siena
Issue date:	2008-08-06
Papers:	22

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NEP is sponsored by SUNY Oswego

In this issue we have:

1. The Locus of Innovation in Small and Medium-sized Firms: The Importance of Social Capital and Networking in Innovative Entrepreneurship
   Hulsink, W.; Elfring, T.; Stam, W.
2. Bridging, linking, and bonding social capital in collective action: The case of Kalahan Forest Reserve in the Philippines
   Dahal, Ganga Ram; Adhikari, Krishna Prasad
3. Shocks, groups, and networks in Bukidnon, Philippines:
   Quisumbing, Agnes R.; McNiven, Scott; Godquin, Marie
4. Social Capital and Basic Goods: The Cautionary Tale of Drinking Water in India
   Sripad Motiram; Lars Osberg
5. A Social Network Analysis of Occupational Segregation
   Marco J. van der Leij; I. Sebastian Buhai
6. Escaping poverty traps?: Collective action and property rights in post-war rural Cambodia
   Weingart, Anne; Kirk, Michael
7. Corruption and Political Interest: Empirical Evidence at the Micro Level
   Benno Torgler; Bin Dong
8. Altruism, Partner Choice, and Fixed-Cost Signaling
   Andriy Zapechelnyuk; Ro’i Zultan
9. Collective action and vulnerability: Burial societies in rural Ethiopia
   Dercon, Stefan; Hoddinott, John; Krishnan, Pramila; Woldehannnam, Tassew
10. Satisfaction with Democracy and Collective Action Problems: The Case of the Environment
    Halla, Martin; Schneider, Friedrich; Wagner, Alexander F.
11. Social Polarization: Introducing distances between and within groups
    Iñaki Permanyer
12. Property rights, collective Action, and poverty: The role of institutions for poverty reduction
    Gregorio, Monica Di; Hagedorn, Konrad; Kirk, Michael; Korf, Benedikt; McCarthy, Nancy; Meinzen-Dick, Ruth; Swallow, Brent
13. Tracing power and influence in networks: Net-Map as a tool for research and strategic network planning
    Schiffer, Eva; Waale, Douglas
14. Collective action to secure property rights for the poor: A case study in Jambi Province, Indonesia
    Komarudin, Heru; Siagian, Yuliana L.; Colfer, Carol J. Pierce; Neldysavrino; Yentirizal; Syamsuddin; Irawan, Deddy
15. Peer effects in public contributions: theory and experimental evidence
    Coralio Ballester; Pablo Brañas-Garza; María Paz Espinosa
16. Collective action initiatives to improve marketing performance: Lessons from farmer groups in Tanzania
    Barham, James; Chitemi, Clarence
17. Attendance to cultural events and spousal influences: the Italian case
    Elisabetta Lazzaro; Carlofilippo Frateschi
18. Development under conditions of inequality and distrust: Social cohesion in Latin America
    Ferroni, Marco; Mateo, Mercedes; Payne, Mark
19. Do Women Pay More for Credit? Evidence from Italy
    Alberto F. Alesina; Francesca Lotti; Paolo Emilio Mistrulli
20. Opportunity and Choice in Social Networks
    Paolo Pin; Silvio Franz; Matteo Marsili
21. Weight Gain in Adolescents and Their Peers
    Halliday, Timothy; Kwak, Sally
22. Self-Regulation by Associations: Collective Action Problems in European Environmental Regulation
    Adrienne HERITIER; Sandra ECKERT

Contents.

1. The Locus of Innovation in Small and Medium-sized Firms: The Importance of Social Capital and Networking in Innovative Entrepreneurship

   Date:	2008-07-21
   By:	Hulsink, W. Elfring, T. Stam, W. (Erasmus Research Institute of Management (ERIM), RSM Erasmus University)
   URL:	http://d.repec.org/n?u=RePEc:dgr:eureri:1765012873&r=soc
   Social networks matter in the innovation processes of young and small firms, since ‘innovation does not exist in a vacuum (Van De Ven, 1986: 601).’ The contacts a firm has could both generate advantages for further innovation and growth, and disadvantages leading to inertia and stagnation. In the first case the existing social network or the new business contact provides opportunities furthering eventual success, in the second case, the existing network or the new business contacts turns out to have a constraining or even detrimental effect on performance. The search and use of social capital is driven by goal-specificity: it only includes those ties that help the actor in the attainment of particular goals. Most of the research so far has been deliberately or unwillingly one-sided, by for instance only looking at entrepreneurial firms in dynamic industries (or more specifically, start-ups in the high-tech industries). Or selective attention has been paid to either the internal sources or the external contacts to trigger innovation. And when a conclusive study has been conducted into investigating both the effect of internal and external ties on innovation, the sample often includes large and established companies and managers (instead of entrepreneurs and smaller firms, as what we are interested in). The main line of reasoning in this paper is as follows. In the first section we discuss the key network concepts, such as, social capital, relational embeddedness (strong and weak ties), structural embeddedness (i.e. structural holes). Section two deals with innovation and the central role of knowledge in the discovery and realisation of innovations. Social networks and its potential for knowledge brokering appear to be important and therefore the last section focuses on the relationship between particular network characteristics and innovation.
   Keywords:	entrepreneurship;innovation;social capital;networking;small- and medium-sized firms;James Dyson

2. Bridging, linking, and bonding social capital in collective action: The case of Kalahan Forest Reserve in the Philippines

   Date:	2008
   By:	Dahal, Ganga Ram Adhikari, Krishna Prasad
   URL:	http://d.repec.org/n?u=RePEc:fpr:worpps:79&r=soc
   “This paper seeks to identify the factors which are responsible for successful management of natural resources when communities are given opportunities to manage those resources. Applying the social capital framework, it analyzes empirical data from the well known case of Kalahan Educational Foundation, the Philippines. The study confirms previous findings, which have emphasized the high level of cohesion and traditional norms among a homogeneous community of indigenous peoples (bonding social capital) as a success factor. This study further identifies that for effective management of collective action, mobilization of bridging and linking social capital are equally important as they do not only help mobilize external resources but, at times, also promote bonding social capital.” authors’ abstract
   Keywords:	Kalahan, People’s Organization (PO), Bonding, Bridging, Linking social capital, Governance, Collective action, Environmental risk,

3. Shocks, groups, and networks in Bukidnon, Philippines:

   Date:	2008
   By:	Quisumbing, Agnes R. McNiven, Scott Godquin, Marie
   URL:	http://d.repec.org/n?u=RePEc:fpr:worpps:84&r=soc
   “This study examines the role of groups and networks in helping poor Filipinos manage their exposure to risks and cope with shocks. It brings together two strands of literature that examine how social capital affects economic variables and investigate the processes by which social capital formation, participation in networks and groups, and trusting behavior comes about. Using a longitudinal study from a province in Northern Mindanao, Philippines, the authors find that households belong to a number of formal and informal groups and networks, but participation differs according to household characteristics. Households belonging to the lower asset quartiles belong to fewer groups, and households with more human and physical capital have larger social networks. Furthermore, wealthier households are more likely to take part in productive groups while membership in civic and religious groups is not limited by economic status. Migrant networks play an important risk-smoothing role via remittances sent by migrant daughters.” authors’ abstract
   Keywords:	Social networks, Groups, Social capital, Poverty, Participation, Gender,

4. Social Capital and Basic Goods: The Cautionary Tale of Drinking Water in India

   Date:	2008-07-21
   By:	Sripad Motiram Lars Osberg (Department of Economics, Dalhousie University) (Department of Economics, Dalhousie University)
   URL:	http://d.repec.org/n?u=RePEc:dal:wparch:social_capital.pdf&r=soc

5. A Social Network Analysis of Occupational Segregation

   Date:	2008-03
   By:	Marco J. van der Leij (University of Alicante) I. Sebastian Buhai (University of Alicante)
   URL:	http://d.repec.org/n?u=RePEc:fem:femwpa:2008.31&r=soc
   We develop a social network model of occupational segregation between different social groups, generated by the existence of positive inbreeding bias among individuals from the same group. If network referrals are important for job search, then expected homophily in the contact network structure induces different career choices for individuals from different social groups. This further translates into stable occupational segregation equilibria in the labor market. We derive the conditions for wage and unemployment inequality in the segregation equilibria and characterize first and second best social welfare optima. Surprisingly, we find that socially optimal policies involve segregation.
   Keywords:	Social Networks, Homophily, Inbreeding Bias, Occupational Segregation, Labor Market Inequality, Social Welfare
   JEL:	J24 J31 J70 Z13

6. Escaping poverty traps?: Collective action and property rights in post-war rural Cambodia

   Date:	2008
   By:	Weingart, Anne Kirk, Michael
   URL:	http://d.repec.org/n?u=RePEc:fpr:worpps:89&r=soc
   “This paper introduces and applies an analytical framework to study how formal and informal institutions influence socio-economic change and poverty reduction in rural Cambodia, giving specific reference to property rights and collective action. It focuses on emerging endogenous mechanisms of cooperation as well as on the role of external actors and instruments in forming or enhancing collective action institutions, and enforcing use and ownership rights among the rural poor. Within this framework key contextual factor, such as asset endowments, legal structures, and power relations, have an impact on poverty and rural livelihoods, but are also mediated and changed by property right regimes and local cooperation. Findings indicate that access to and use of natural capital still contributes significantly to rural incomes. Access to natural resources is, however, defined by multiple and overlapping rights, both private and common ones, which are, in turn, governed by formal and informal patterns of cooperation. Collective action also contributes to improve livelihoods. Nevertheless, depending on asset endowments, differences exist in the degree of participation. Owing to Cambodia’s recent history of genocide, forced collectivization and resettlement, property rights regimes have been severely affected, remain contested, and are re-established only slowly. In this context, the mutual trust necessary for successful cooperation in common property issues is severely undermined.” authors’ abstract
   Keywords:	Collective action, Property rights, Post-war, Rural development, Livelihoods,

7. Corruption and Political Interest: Empirical Evidence at the Micro Level

   Date:	2008-04
   By:	Benno Torgler (Queensland University of Technology) Bin Dong (Queensland University of Technology)
   URL:	http://d.repec.org/n?u=RePEc:fem:femwpa:2008.39&r=soc
   The topic of corruption has recently attracted a great deal of attention, yet there is still a lack of micro level empirical evidence regarding the determinants of corruption. Furthermore, the present literature has not investigated the effects of political interest on corruption despite the interesting potential of this link. We address these deficiencies by analyzing a cross-section of individuals, using the World Values Survey. We explore the determinants of corruption through two dependent variables (perceived corruption and the justifiability of corruption). The impact of political interest on corruption is explored through three different proxies, presenting empirical evidence at both the cross-country level and the within-country level. The results of the multivariate analysis suggest that political interest has an impact on corruption controlling for a large number of factors.
   Keywords:	Corruption, Political Interest, Social Norms
   JEL:	K42 D72 O17 J24

8. Altruism, Partner Choice, and Fixed-Cost Signaling

   Date:	2008-07
   By:	Andriy Zapechelnyuk Ro’i Zultan
   URL:	http://d.repec.org/n?u=RePEc:huj:dispap:dp483&r=soc
   We consider a multitype population model with unobservable types, in which players are engaged in the `mutual help’ game: each player can increase her partner’s fitness at a cost to oneself. All individuals prefer free riding to cooperation, but some of them, helpers, can establish reciprocal cooperation in a long-term relationship. Such heterogeneity can drive cooperation through a partner selection mechanism under which helpers choose to interact with one another and shun non-helpers. However, in contrast to the existing literature, we assume that each individual is matched with an anonymous partner, and therefore, stable cooperation cannot be achieved by partner selection per se. We suggest that helpers can signal their type to one another in order to establish long-term relationships, and we show that a reliable signal always exists. Moreover, due to the difference in future benefits of a long-term relationship for helpers and non-helpers, the signal need not be a handicap, in the sense that the cost of the signal need not be correlated with type.

9. Collective action and vulnerability: Burial societies in rural Ethiopia

   Date:	2008
   By:	Dercon, Stefan Hoddinott, John Krishnan, Pramila Woldehannnam, Tassew
   URL:	http://d.repec.org/n?u=RePEc:fpr:worpps:83&r=soc
   “Collective action can help individuals, groups, and communities achieve common goals, thus contributing to poverty reduction. Drawing on longitudinal household and qualitative community data, the authors examine the impact of shocks on household living standards, study the correlates of participation in groups and formal and informal networks, and discuss the relationship of networks with access to other forms of capital. In this context, they assess how one form of collective action, iddir, or burial societies, help households attenuate the impact of illness. They find that iddir effectively deal with problems of asymmetric information by restricting membership geographically, imposing a membership fee, and conducting checks on how the funds were spent. The study also finds that while iddir help poor households cope with individual health shocks, but shows that the better-off households belong to more groups and have larger networks. In addition, where households have limited ability to develop spatial networks, collective action has limited ability to respond to covariate shocks. Therefore, realism is needed in terms of the ability of collective action to respond to shocks, and direct public action is more appropriate to deal with common shocks.” authors’ abstract
   Keywords:	Collective action, Burial societies, Shocks, Vulnerability, Poverty, Networks,

10. Satisfaction with Democracy and Collective Action Problems: The Case of the Environment

    Date:	2008-07
    By:	Halla, Martin (University of Linz) Schneider, Friedrich (University of Linz) Wagner, Alexander F. (University of Zurich)
    URL:	http://d.repec.org/n?u=RePEc:iza:izadps:dp3613&r=soc
    Using modern methods for analyzing multi-level data, we find that, by and large, citizens of OECD countries are more satisfied with the way democracy works in their country if more environmental policies are in place and if environmental quality is higher. We also document that parents care about carbon dioxide emissions more than non-parents and that those with a high willingness to pay for environmental quality deplore intervention through government policies.
    Keywords:	satisfaction with democracy, environmental economics and policy, collective action problems
    JEL:	K32 P16 Q21 Q28

11. Social Polarization: Introducing distances between and within groups

    Date:	2008-07-14
    By:	Iñaki Permanyer
    URL:	http://d.repec.org/n?u=RePEc:aub:autbar:751.08&r=soc
    The measurement of social polarization has received little attention from the literature. The only social polarization index that has been used to measure religious or ethnic polarization (the RQ index) has several shortcomings that are critically discussed in the paper. In particular, that index is not taking into account the existing distance between and within different groups. A couple of axiomatically characterized social polarization indices that overcome these limitations are presented. In the empirical section we show that the rankings of countries according to the levels of polarization change to a great extent when we replace the RQ index by the indices presented in this paper.

12. Property rights, collective Action, and poverty: The role of institutions for poverty reduction

    Date:	2008
    By:	Gregorio, Monica Di Hagedorn, Konrad Kirk, Michael Korf, Benedikt McCarthy, Nancy Meinzen-Dick, Ruth Swallow, Brent
    URL:	http://d.repec.org/n?u=RePEc:fpr:worpps:81&r=soc
    “This paper presents a conceptual framework on how institutions of property rights and collective action can contribute to poverty reduction, including through external interventions and action by poor people themselves. The first part of the paper examines the initial conditions of poverty, highlighting the role of assets, risks and vulnerability, legal structures and power relations. The latter part investigates the decision-making dynamics of actors—both poor and non-poor—and how they can use the tangible and intangible resources they have to shape their livelihoods and the institutions that govern their lives. The paper concludes with a discussion of how attention to property rights and collective action can improve the understanding of outcomes in terms of changes in wellbeing.” authors’ abstract
    Keywords:	Collective action, Property rights, Poverty reduction, Conceptual framework, Vulnerability, Power, Institutions, Wellbeing,

13. Tracing power and influence in networks: Net-Map as a tool for research and strategic network planning

    Date:	2008
    By:	Schiffer, Eva Waale, Douglas
    URL:	http://d.repec.org/n?u=RePEc:fpr:ifprid:772&r=soc
    “Believing that complex problems call for complex solutions and that stakeholders should have a say in policies that concern them, policymakers have strongly promoted the development of forums and organizations made up of many stakeholders to address complex governance issues such as water management. Both developing and developed countries have instituted multistakeholder water governance bodies on local, national, and international levels. However, while the belief is strong that these integrated bodies should improve governance, how and to what extent that actually happens is still unclear, not only because of the complexity of the matter but also due to a lack of appropriate research tools for the analysis of complex governance systems. This paper presents an innovative empirical research tool—Net-Map—developed to better understand multistakeholder governance by gathering in-depth information about governance networks, goals of actors, and their power and influence. Researchers and implementers alike can use Net-Map to collect qualitative and quantitative information in a structured and comparable way. It can be used both as a research tool and as an instrument for organizational development and strategic network planning. A case study on the development of a multistakeholder water governance body in northern Ghana illustrates the application of this research method. The method can be used on many different levels, from the community, to national or even international levels. Net-Map merges characteristics of two existing methods, namely social network analysis and the power mapping tool. Using a participatory approach, interviewees and interviewers together draw a network map of the actors involved in the policy arena and characterize the different kinds of links between the actors. They then add “influence towers,” made of checkers pieces, to transfer the abstract concepts of power and influence into a three-dimensional form. Finally, the interviewee assesses the goal orientation of the different actors (for example, developmental versus environmental or pro versus con a certain intervention). The tool provides an influence network map of the governance situation as well as qualitative and quantitative data about the perceived power and influence of the actors. While the data lend themselves to complex quantitative analysis, this paper mainly focuses on the use of the tool for the purpose of mapping and organizational development. The paper explores how the mapping process itself also stimulates a structured in-depth discussion of crucial issues and ways forward. In Ghana, the method has proven to be interculturally applicable and easy to apply and adapt. Interviewees were excited about their own learning processes throughout the interview. Implicit understanding and concepts were visualized and made explicit so that group members could understand where they agree and differ in their perception of the governance arena.” from Author’s Abstract
    Keywords:	Water governance, Social network analysis, Net-Map, Research methodology, Multi-stakeholder governance,

14. Collective action to secure property rights for the poor: A case study in Jambi Province, Indonesia

    Date:	2008
    By:	Komarudin, Heru Siagian, Yuliana L. Colfer, Carol J. Pierce Neldysavrino Yentirizal Syamsuddin Irawan, Deddy
    URL:	http://d.repec.org/n?u=RePEc:fpr:worpps:90&r=soc
    “This study presents an approach to analyzing decentralized forestry and natural resource management and land property rights issues, and catalyzing collective action among villages and district governments. It focuses on understanding the current policies governing local people’s access to property rights and decision making processes, and learning how collective action among community groups and interaction among stakeholders can enhance local people’s rights over lands, resources, and policy processes for development. The authors applied participatory action research in two villages, one each in the Bungo and Tanjabbar districts of Jambi province (Sumatra), Indonesia, to facilitate identification of priorities through phases of planning, action, monitoring, and reflecting. This study finds that action research may be an effective strategy for fostering collective action and maintaining the learning process that leads groups to be more organized and cohesive, and district government officials to be more receptive to stakeholders. A higher level of collective action and support may be needed to avoid elite capture more effectively.” authors’ abstract
    Keywords:	Decentralization, Natural resource management, Forest, Collective action, Property rights, Action research, Poverty, Devolution,

15. Peer effects in public contributions: theory and experimental evidence

    Date:	2008-06-27
    By:	Coralio Ballester (Department of Economics, University of Alicante.) Pablo Brañas-Garza (Department of Economic Theory and Economic History, University of Granada.) María Paz Espinosa (Universidad del País Vasco)
    URL:	http://d.repec.org/n?u=RePEc:gra:wpaper:08/04&r=soc
    This paper analyzes the impact of social integration on cooperative behavior. We show that if the social network shows assortative mixing then conditional cooperation is an equilibrium strategy for altruistic subjects with a high degree of social integration.We provide experimental evidence on the relationship between individuals’ position in a social network and their contributions in a public good game.
    Keywords:	public good game, social networks, conditional cooperation.
    JEL:	C91 D64 C72 H41

16. Collective action initiatives to improve marketing performance: Lessons from farmer groups in Tanzania

    Date:	2008
    By:	Barham, James Chitemi, Clarence
    URL:	http://d.repec.org/n?u=RePEc:fpr:worpps:74&r=soc
    “The primary inquiry of this study is to identify and understand the underlying factors that enable smallholder farmer groups to improve their market situation. The specific objective of this paper is to examine to what extent certain group characteristics and asset endowments facilitate collective action initiatives to improve group marketing performance. This objective is approached through an evaluation of a government-led program in Tanzania, which is attempting to increase smallholder farmers’ incomes and food security through a market-oriented intervention. Findings suggest that more mature groups with strong internal institutions, functioning group activities, and a good asset base of natural capital are more likely to improve their market situation. Gender composition of groups also factors in group marketing performance. It acts as an enabling factor for male-dominated groups and as a disabling factor for female-only groups. Structural social capital in the form of membership in other groups and ties to external service providers, and cognitive social capital in the form of intragroup trust and altruistic behavior are not significant factors in a group’s ability to improve its market situation.” authors’ abstract
    Keywords:	Collective action, Agricultural marketing, Farmer groups, Social capital, Planned change initiatives, Gender, Marketing,

17. Attendance to cultural events and spousal influences: the Italian case

    Date:	2008-07
    By:	Elisabetta Lazzaro (University of Padua) Carlofilippo Frateschi (University of Padua)
    URL:	http://d.repec.org/n?u=RePEc:pad:wpaper:0084&r=soc
    In cultural consumption it is quite reasonable to expect that the formation and the evolution of preferences, and the related individual choice behaviour, is affected by various interactions within families, peer and other social groups. Our investigation focuses on a specific form of “indirect” interaction effect, that is the reciprocal influence that a married person’s preferences and characteristics can have on the cultural consumption of her/his partner. Using the last two available nationwide crosssection datasets on the leisure activities of the Italian population (ISTAT, 1995 and 2000), we estimate the mutual influence of spouses’s educational and cultural background, besides other factors, on the consumption of three kinds of cultural activities, namely museum/exhibition, theatre, and opera and classical music concerts.
    Keywords:	Mutual social interactions, cultural consumption
    JEL:	D79 D12 Z11

18. Development under conditions of inequality and distrust: Social cohesion in Latin America

    Date:	2008
    By:	Ferroni, Marco Mateo, Mercedes Payne, Mark
    URL:	http://d.repec.org/n?u=RePEc:fpr:ifprid:777&r=soc
    “This paper analyzes the role of social cohesion in economic and institutional development and, broadly, the creation of welfare in Latin America. The paper defines the concept of social cohesion with reference to the notions of social capital and inequality. Using data and literature on Latin America, the paper argues that low interpersonal trust and entrenched inequality interfere with cohesion. The paper develops and introduces an exploratory index of cohesion structured around the definition proposed. Relying on correlations, and with appropriate caveats, the paper uses this index to explore tentative linkages between levels of cohesion and development outcomes. The paper presents evidence of positive linkages among social cohesion and economic growth, investment and innovation capacity, governmental effectiveness, the quality of public policies, and the predictability of the policy environment. Finally, the paper discusses the significance of these findings and some of the policy implications.” from Author’s Abstract
    Keywords:	Social cohesion, Social capital, Trust, Inequality, Exclusion, Opportunities, Governance, Institutional development, economic growth, Development strategies,

19. Do Women Pay More for Credit? Evidence from Italy

    Date:	2008-07
    By:	Alberto F. Alesina Francesca Lotti Paolo Emilio Mistrulli
    URL:	http://d.repec.org/n?u=RePEc:nbr:nberwo:14202&r=soc
    The answer is yes. By using a unique and large data set on overdraft contracts between banks and microfirms and self-employed individuals, we find robust evidence that women in Italy pay more for overdraft facilities than men. We could not find any evidence that women are riskier then men. The male/female differential remains even after controlling for a large number of characteristics of the type of business, the borrower and the market structure of the credit market. The result is not driven by women using a different type of bank than men, since the same bank charges different rates to male and female borrowers. Social capital does play a role: high levels of trust loosen credit conditions by lowering interest rates, but this benefit is not evenly distributed, as women benefit from increased social capital less than men.
    JEL:	G21 J16 J71

20. Opportunity and Choice in Social Networks

    Date:	2008-03
    By:	Paolo Pin (Università Ca’ Foscari di Venezia) Silvio Franz (Universite Paris-Sud 11) Matteo Marsili (The Abdus Salam International Centre for Theoretical Physics)
    URL:	http://d.repec.org/n?u=RePEc:fem:femwpa:2008.24&r=soc
    Our societies are heterogeneous in many dimensions such as census, education, religion, ethnic and cultural composition. The links between individuals - e.g. by friendship, marriage or collaboration - are not evenly distributed, but rather tend to be concentrated within the same group. This phenomenon, called imbreeding homophily, has been related to either (social) preference for links with own–type individuals ( choice-based homophily) or to the prevalence of individuals of her same type in the choice set of an individual ( opportunity-based homophily). We propose an indicator to distinguish between these effects for minority groups. This is based on the observation that, in environments with unbiased opportunities, as the relative size of the minority gets small, individuals of the minority rarely meet and have the chance to establish links together. Therefore the effect of choice–based homophily gets weaker and weaker as the size of the minority shrinks. We test this idea across the dimensions of race and education on data on US marriages, and across race on friendships in US schools, and find that: for what concerns education i) opportunity–based homophily is much stronger than choice–based homophily and ii) they are both remarkably stationary in time; concerning race iii) school friendships do not exhibit opportunity-based homophily, while marriages do, iv) choice-based homophily is much stronger for marriages than for friendships and v) these effects vary widely across race.
    Keywords:	Social Networks, Choice-Based and Opportunity-Based Homophily
    JEL:	D85 J11 J12

21. Weight Gain in Adolescents and Their Peers

    Date:	2008-07
    By:	Halliday, Timothy (University of Hawaii at Manoa) Kwak, Sally (University of Hawaii at Manoa)
    URL:	http://d.repec.org/n?u=RePEc:iza:izadps:dp3610&r=soc
    Despite the urgent public health implications, relatively little is yet known about the effect of peers on adolescent weight gain. We describe trends and features of adolescent BMI in a nationally representative dataset and document correlations in weight gain among peers. We find strong correlations between own body mass index (BMI) and peers’ BMI’s. Though the correlations are especially strong in the upper ends of the BMI distribution, the relationship is smooth and holds over almost the entire range of adolescent BMI. Furthermore, the results are robust to the inclusion of school fixed effects and basic controls for other confounding factors such as race, sex, and age. Some recent research in this area asks whether or not adolescent weight gain is caused by peers. We discuss the econometric difficulties in plausibly estimating such effects. Our results do not rule out the existence of these types of social network effects.
    Keywords:	obesity, peer effects, adolescent health
    JEL:	I10 I12

22. Self-Regulation by Associations: Collective Action Problems in European Environmental Regulation

    Date:	2008-07-17
    By:	Adrienne HERITIER Sandra ECKERT
    URL:	http://d.repec.org/n?u=RePEc:rsc:rsceui:2008/26&r=soc
    How and to what effect do firms coordinate their actions in order to deal with the negative external effects of productive activity? Under which conditions do firm associations engage in environmental self-regulation and what kind of governance devices do they develop in order to tackle the specific regulatory challenges at stake? Is the ’shadow of hierarchy’, the credible threat of legislation, executive intervention or court rulings, a necessary condition for associative action to emerge? Or is it only necessary if a redistributive problem is at stake? These are the questions discussed in this article. We will first develop the theoretical argument based on economic institutionalism, derive hypotheses and then submit the propositions to a first empirical assessment of associative self-regulation on waste recycling in the plastic and paper industry.
    Keywords:	governance; self-regulation; shadow of hierarchy; transaction cost theory.