This study examines some of the prominent state tax rankings that have been developed in recent years, with a focus on the indices that are specifi cally attempting to measure state and local taxes in some way. Each index is reviewed to determine what aspect of state tax systems are being measured and how. The article begins with a theoretical framework that informs the question of what tax rates should be measured, depending on the purpose of the intended index. It is important to distinguish,

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... for example, whether tax rates are measured as average tax rates, marginal tax rates, statutory tax rates, or effective marginal tax rates. After analysis of the way several prototypical indices are constructed, this study also considers whether the indices actually have economic explanatory power. The Tax Foundation's State Business Tax Climate Index is used as an explanatory variable in several estimated state GDP growth models. While the index has a statistically signifi cant effect on state GDP growth in simple models, once more state-specifi c factors are included in the growth models the signifi cance of the index disappears. Research suggestions are made for techniques that can be used to more effectively assess the explanatory power of state tax rankings. The conclusion of the analysis is that caution on the use and interpretation of such indices is warranted.