In our context, we have both a linear public good (cleanliness) and a threshold public good (lack of flooding). As we are most interested in a reduction in flooding, the literature on threshold public goods is particularly relevant. In the case of a threshold public good, an efficient equilibrium can exist where the public good is provided. However, an inefficient equilibrium with zero contributions to the public good also exists. In this paper, we seek to investigate whether it is possible to shift a large community that is stuck in an inefficient equilibrium towards the efficient one, by targeting a key subgroup within the community. While threshold public goods games have been tested in laboratory experiments, the literature on testing these kinds of interventions in the field is much sparser.<sup>3</sup> The design of our intervention draws on a number of findings in the literature related to behavior in public goods games. Firstly, a higher threshold has been shown to discourage contributions (Cadsby and Maynes, 1999) while higher step returns to the public good have been found to increase contributions (Croson and Marks, 2000). In our intervention, by providing incentives for CBO members to achieve a clean neighborhood, the return for members to achieving the threshold is increased and also the level of threshold required to receive a reward is reduced (relative to the threshold required to reduce flooding). Secondly, other factors that have been shown to be important for successful provision are the size of the group (Croson and Marks, 2000; Feltovich and Grossman, 2015) and the degree of interconnection of group members (Ostrom, 2009). As this intervention is targeted at existing CBOs, the size of the group that must work together to contribute to the public good is smaller than the community as a whole and is also a group that has a high level of existing social capital. Finally, the existence of leaders and coalitions can help to increase the provision of the public good, although this also depends on the returns to members of the coalition, and the likelihood of free-riding by non-members (Moxnes and van der Heijden, 2003; Gächter and Renner, 2018; Bosettia et al., 2017). The CBOs in our context can play a leadership role within the community where their actions are highly observable by other community members, potentially shifting beliefs about the equilibrium and thereby encouraging contributions by non-members. We contribute to this literature by providing evidence from an RCT that these types of mechanisms can be effective at overcoming the public goods problem in a denselypopulated urban setting.

Our paper also contributes to the body of literature exploring the role of CBOs in the implementation of development programs, in particular in relation to public goods provision. The 2004 World Development Report (World Bank, 2004) highlighted the need for community-level engagement to solve collective action problems. In general, the evidence on the effectiveness of community-based approaches in the provision and maintenance of public goods is mixed. There are some examples of such approaches having a positive effect on access to water and sanitation (Beath et al., 2013; Guiteras et al., 2015), but evidence on projects that aim to address the maintenance of public infrastructure is scarce. As highlighted by Mansuri and Rao (2004), the success of such projects will depend on the specific context, the time horizon, and the design of the community-based scheme. Moreover, recent evidence from randomized control trials of community-based interventions suggests that the mechanisms for effective collective action will also depend on the context and type of public good in question. Support for grassroots community-level engagement as opposed to involving local authorities is provided by Sheely (2013) for the case of anti-littering in Kenya. In contrast, Jack and

> 3 One exception is Carlsson et al. (2015) which investigates the impact of different strategies for eliciting contributions to a real threshold public good (a bridge) in Vietnam. They find significant effects of both social influence and defaults on the size of contributions but only when the reference or default contributions are low.

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