The objective of this study was to explore a new method of analyzing the performance of substate economies. Conventional analyses of economic diversity and growth are limited by their reliance on static measures of economic structure. Such measures do not capture the patterns of growth dynamics or structural change a region may be experiencing. This paper discusses a new measure of dynamic economic diversity and explores its relationship to economic performance. The measure is a statistical index that reflects the degree to which employment in a county's industries move together, over time. The more the industries' employment levels move together the higher the index value, which hypothetically indicates a higher degree of regional economic integration. The analysis was applied to county-level data from three states: Iowa, Minnesota, and Wisconsin. The findings were: (1) Metro(politan) areas showed the highest values of the dynamic coherence index, and farm counties had the lowest values. Non-farm/non-metro counties were in the middle range; (2) High-coherence counties tend to have higher levels of per-capita income; and (3) Dynamic coherence appears to be positively related to the rate of economic growth as measured by employment growth rates. These findings may indicate that conventional static measures do not capture the economic linkages between industry sectors that make them move together. The correlations between the index of dynamic coherence, income growth, and employment growth may reflect the importance of interindustry linkages to the growth process. (Author/TES)