Well, what do you classify as economic freedom? This term is used to mean many things & is always taken out of context completely.You need to question if what you read is true.
Bennett, Daniel, and Richard Vedder. "A dynamic analysis of economic freedom and income inequality in the 50 US states: Empirical evidence of a parabolic relationship." (2012).
By this I mean, Capitalism says Capitalism means Free Markets, but it doesn't. US says they are for freedom, democracy, but they aren't. Just reading something doesn't make it true.
Also, it seems like capitalist countries have freer markets than communist/socialist ones. Though you’d have to give examples of communist/socialist countries.
Generally they have many categories. Rate the market conditions on a scale (some of the measures are quantitative). Average the ratings together to get one number comparing countries