Here is what Robert Dahl had to say about measuring political equality:
According to Dahl, in On Political Equality:
MEASURING POLITICAL EQUALITY p. 78
“Achieving truly well-grounded judgments about the future of political equality in the united states probably exceeds our capacities. One reason is that, unlike income or wealth, or even health, longevity, and other possible ends, to estimate gains and losses in political equality we lack cardinal measures that would allow us to say, for example, that “political equality is twice as great in country X as in country Y.” At best we must rely on ordinal measures based on judgments about ‘more,’ ‘less,’ ‘about the same,’ and the like.”
He goes on to say that we might be able to develop ordinal measures by qualified observers to ascertain measures of more, less, or about the same.