One strand has looked at the effects of aggregate infrastructure stocks and service flows on per capita GDP. This includes a majority of the macroeconomic studies, which look at expansion paths of per capita sectoral stocks with per capita GDP, thereby identifying countries that are outliers in terms of infrastructure investments in middle- and low-income regions (Ingram and Fay, 2008). Another strand has examined the effects of specific kinds of infrastructure interventions on growth and poverty reduction, usually focusing on particular geographical areas, enterprises or sectors (Straub, 2008).