such as test scores, are statistically significantly associated with higher growth.<sup>26</sup> This is especially true for LICs (Hanushek, Ruhose, and Woessmann 2017a, 2017b).

Other factors can slow human capital accumulation or dampen its growth-enhancing effects. These include unsupportive household environments (Hanushek 2002; Woessmann 2003a). It also includes weak institutional environments that can divert highly skilled labor into unproductive activities such as rent-seeking.<sup>27</sup> Similarly, a stagnating economy with limited job creation may struggle to employ productively a better educated workforce and thus fail to reap the full gains in terms of growth (World Bank 2018c). Some studies find evidence of self-reinforcing feedback loops from higher growth to higher investment in human capital.<sup>28</sup> Health, nutrition, and growth: Empirical evidence. Both at the individual worker level and at the country level, improved health has been found to be associated with greater productivity and higher incomes. Early childhood interventions appear to be particularly beneficial (Grantham-McGregor et al. 2007). For children, better nutrition has been associated with better educational performance and, once they enter the labor market, higher incomes.<sup>29</sup> As with education, there appear to be positive feedback loops as higher incomes allow more investment into healthcare and related infrastructure (Weil 2014).

# Infrastructure and growth

Conceptual links. Like human capital accumulation, infrastructure investment can raise output growth both directly through growth of the capital stock, which is a factor of production, and indirectly through its collateral benefits for TFP growth. Good infrastructure investment can encourage innovation and knowledge diffusion, enhance human capital and TFP, and thus lower production costs, improve a country’s international competitiveness, and facilitate trade (Agenor 2013; Demetriades and Mamuneas 2000). For example, better transportation networks can reduce the cost of, and time taken in, new construction and the installation of new equipment (Turnovsky 1996), while improved access to electricity and better sanitation can help to raise educational attainment and public health standards (Agenor 2011; Getachew 2010). The growth-enhancing effects of infrastructure investment depend on its quality and, for some types of infrastructure investment, the interconnectedness of networks and freedom from congestion.<sup>30</sup> Infrastructure investment and growth: Empirical evidence. Studies of the effects of infrastructure investment spending typically find that it raises output, but only modestly and without accompanying productivity increases (Straub and Terada-Hagiwara 2010).<sup>31</sup>

> 26 See Hanushek and Kimko (2000) and Hanushek and Woessmann (2015a, 2015b, 2016). 27 See Easterly (2001); Pritchett (2001); and Murphy, Shleifer, and Vishny (1991). 28 See Bils and Klenow (2000), Pritchett (2001, 2006), and Weil (2014). 29 See Galasso et al. (2017), Luo et al. (2012), and Taras (2005). 30 See Hulten (1994), OECD (2007), and Sanchez-Robles (1998).

> 31 Surveys of the literature include Pereira and Andraz (2013), Bom and Ligthart (2014), and Romp and