This article quality assures GDP and then links it to well-being in the world’s two largest economies. Despite the global plethora of national indexes, there has been little quality assurance of the unidimensionality of their component indicators. Unidimensional index theory constructs a weighted composite from a 2-level principal components analysis of its several indicators. This weighted composite evaluates its unweighted counterpart, and informs governments about the allocation of resources over its composite indicators. Two axioms predict that weighted and unweighted indexes are perfectly correlated over successive yearly populations in the USA and China. Under these axioms, fractional polynomial regressions of any criterion on these weighted and unweighted indexes perfectly predict this criterion. We confirm the unidimensionality of American and Chinese GDP indexes and their near-perfect prediction of the United Nation’s Human Development Index (HDI). This application discovers that HDI computation can be carried out from a nation’s GDP alone, i.e., without survey sampling, questionnaire interrogation, probabilistic inference, significance testing, or even HDI data.