An OPM study has highlighted how political economy analysis (PEA) can improve the design, implementation and effectiveness of pro-poor sanitation investments and services. According to the Human Development Report 2006, an estimated 2.5 billion people lack access to basic sanitation, predominantly in low- and middle-income countries. While significant progress has been made in addressing this problem, sanitation practitioners have tended to approach the issue from a technical perspective, often overlooking how different stakeholders, along with different social, institutional and economic processes, influence each other and, ultimately, sanitation outcomes.