Chong et al. (2008) found only limited support for the income convergence hypothesis among 15 OECD nations using a nonlinear unit root test. We find considerably greater evidence of convergence by allowing for breaks in the test's time trend.

The results of previous time-series studies of the income convergence hypothesis indicate that practically no African economies are systematically closing their income gap with the rich world. This implies that almost the entire continent is not ‘developing’ in the literal sense of the term....