Stefan Karlsson of the Ludwig von Mises Institute challenged the usefulness of the index due to the fuzziness of many of the categories used to determine freedom. John Miller roundly criticizes the "Index", writing in "Dollars & Sense", "In the hands of the Wall Street Journal and the Heritage Foundation, Washington's foremost right-wing think tank, however, an economic freedom index merely measures corporate and entrepreneurial freedom from accountability. Upon examination, the index turns out to be a poor barometer of either freedom more broadly construed or of prosperity." According to Left Business Observer, growth in Index accounts for 10% of the variation in the growth of GDP.