We document the presence of multiple and varied constraints to small and medium firm growth. This presents both a practical problem for business training programs and a challenge to academic economists trying to identify mechanisms though which these programs may affect outcomes. External validity needs theory. This pushes researchers to narrowly defined and highly selected sample frames, which limits the potential for clear, generalizable policy prescriptions. Ultimately, larger samples, multi-arm evaluations, process documentation, and narrowly-focused, theory-supported empirical work are all needed, but the complexity of the problem limits what we learn from any single study.

We use the Becker-DeGroot-Marschak (BDM) mechanism to estimate willingness to pay (WTP) for and heterogeneous impacts of clean water technology through a field experiment in Ghana. Although WTP is low relative to cost, demand is inelastic at low prices. Short-run treatment effects are positive throughout the WTP distribution. After 1 year, use and benefits are both increasing in WTP, with negative effects on low-WTP households. Combining estimated treatment effects with households’ WTP implies valuations of health benefits much smaller than typically used by policy makers. We explore differences between BDM and take-it-or-leave-it valuations and make recommendations for implementing BDM in the field.