Dyadic data are common in the social sciences, although inference for such settings involves accounting for a complex clustering structure. Many analyses in the social sciences fail to account for the fact that multiple dyads share a member, and that errors are thus likely correlated across these dyads. We propose a non-parametric, sandwich-type robust variance estimator for linear regression to account for such clustering in dyadic data. We enumerate conditions for estimator consistency. We also extend our results to repeated and weighted observations, including directed dyads and longitudinal data, and provide an implementation for generalized linear models such as logistic regression. We examine empirical performance with simulations and an application to interstate disputes.

Entrepreneurs in many emerging economies start their firms informally, without registering with the state. We examine how informality at the time of founding affected the performance of 12,146 firms in 18 countries across sub-Saharan Africa. Our findings indicate that entrepreneurs who registered their firms at founding enjoyed greater success in terms of sales and employment. But these benefits varied widely across countries. Consistent with the idea that legitimation processes account for these benefits, countries in which people trust their government more had larger advantages associated with being formal.

Lee Fleming 2,3 C rowdfunding (CF) platforms, such as Kickstarter (KS), offer a means of funding innovation, connecting inventors and entrepreneurs with a multitude of supporters, who each provide a small fraction of the amount required to fund the project. Although considerable funding for innovation has historically come from venture capitalists (VCs), the entrepreneurs funded by VCs often mirror the investors in terms of their educational, social, and professional characteristics and end up concentrated in a small number of regions (1-4). Policy-makers have thus hailed CF platforms, hoping that they will expand access to entrepreneurial finance, including among women and minority innovators, and that the innovations funded will create jobs and spur economic growth (5). But if particular regions, or certain sorts of individuals, routinely produce better ideas (6), and VC concentrates on them, then CF might simply compete with professional investors to fund the same ideas. We find, however, that CF has been funding innovators in a large number of places that have typically been excluded from VC, and has also been expanding the geographic reach of VC itself. We compare data from 2009 to 2015 on KS campaigns and on VC investments [see supplementary materials (SM) for details on all data and analyses]. One of the dif-INSIGHTS POLICY FORUM ENTREPRENEURIAL ECONOMICS Expand innovation finance via crowdfunding Crowdfunding attracts venture capital to new regions

A group of experts discuss their thoughts about the current state of crowdfunding, its future, important emerging trends in the field, and the opportunities and challenges facing investors and entrepreneurs in the space. Across the board, these experts highlight the importance of crowdfunding as a means for mobilizing resources. They also maintain that crowdfunding has already emerged as an important force in global finance, one which appears here to stay, but one where we have only begun to see the ways in which it will transform the financial sector.

Socially and educationally disadvantaged entrepreneurs often lack the knowledge and prior experience to develop and scale their businesses. Owing to limited educational and employment opportunities, poverty, and discrimination, these entrepreneurs frequently experience low business growth and performance. What factors influence the effectiveness of early-stage venture incubation and mentoring for promoting learning, scaling, and profitability among these entrepreneurs? Two studies in a business incubator serving low-income, underprivileged entrepreneurs in South Africa evaluate this question. Study 1 uses a matched, two-period case-control design to investigate the effects of incubation on business growth by comparing selected and incubated companies to similar also-selected but not incubated ones. The findings show that incubated companies grew 22% more in revenue and 15% more in employment than not incubated companies over the six months between applying to and graduating from the incubator. Study 2 uses instrumental-variable models to evaluate the role that mentoring played in improving business performance by analyzing data from seven cohorts of participants in the incubator randomly assigned to mentors. The findings show that participants assigned to high-ability (versus low-ability) mentors had 3.2% higher revenue and 3.5% higher profits one year after incubation. Further, the benefits of being mentored were more significant for businesses whose entrepreneurs had less pre-entry knowledge and experience, suggesting that mentoring supplemented gaps in human capital. These findings have implications for ways to support disadvantaged entrepreneurs and their businesses through mentoring and early-stage venture incubation.

Highlights d We estimate impacts of five mechanisms on nations' CO 2 emissions over 1970-2016 d Without these mechanisms, emissions grow as fast as the economy d Energy system decarbonization was the primary mechanism for high-income countries d Productivity gains were the primary mechanism for lowincome countries

Complex innovations– ideas, practices, and technologies that hold uncertain benefits for potential adopters—often vary in their ability to diffuse in different communities over time. To explain why, I develop a model of innovation adoption in which agents engage in naïve (DeGroot) learning about the value of an innovation within their social networks. Using simulations on Bernoulli random graphs, I examine how adoption varies with network properties and with the distribution of initial opinions and adoption thresholds. The results show that: (i) low-density and high-asymmetry networks produce polarization in influence to adopt an innovation over time, (ii) increasing network density and asymmetry promote adoption under a variety of opinion and threshold distributions, and (iii) the optimal levels of density and asymmetry in networks depend on the distribution of thresholds: networks with high density (>0.25) and high asymmetry (>0.50) are optimal for maximizing diffusion when adoption thresholds are right-skewed (i.e., barriers to adoption are low), but networks with low density (<0.01) and low asymmetry (<0.25) are optimal when thresholds are left-skewed. I draw on data from a diffusion field experiment to predict adoption over time and compare the results to observed outcomes.

Existing research at the nexus of institutional theory and entrepreneurship suggests that lowering institutional barriers to forming, growing, and exiting new firms can affect the types of start-ups that entrepreneurs found in a region. These institutional changes could influence entrepreneurs’ perceptions of the value of partnering with venture accelerators and potentially improve these sponsors’ capacity to select high-growth start-ups to fund and develop. This study evaluates these ideas by developing and testing three hypotheses. First, institutional reforms improve entrepreneurs’ perceived value of venture accelerators for resources that affect new venture development. Second, they reduce the average probability of being selected for new applicants, due to a surge in the number and heterogeneity of new applicants within accelerators’ local ecosystems. Third, institutional reforms increase the quality of selected cohorts for accelerator managers due to increases in the average quality and human capital of new applicants. To evaluate these hypotheses, I analyze data from 13,770 applicants to venture accelerators over multiple application cycles between 2016 and 2018 in 170 countries. I use a differences-in-differences design to estimate the effects of institutional changes on start-up selection after regulatory reforms that reduced the time and procedures to start new firms, obtain credit, and resolve bankruptcy for entrepreneurs. The findings have valuable implications for how governments, especially those in emerging and developing economies, can support high-growth entrepreneurship.