The disposition of a retrieval system to favour certain documents over others can be quantified using retrievability. Typically, the Gini Coefficient has been used to quantify the level of bias a system imposes across the collection with a single value. However, numerous inequality measures have been proposed that may provide different insights into retrievability bias. In this paper, we examine 8 inequality measures, and see the changes in the estimation of bias on 3 standard retrieval models across their respective parameter spaces. We find that most of the measures agree with each other, and that the parameter setting that minimise the inequality according to each measure is similar. This work suggests that the standard inequality measure, the Gini Coefficient, provides similar information regarding the bias. However, we find that Palma index and 20:20 Ratio show the greatest differences and may be useful to provide a different perspective when ranking systems according to bias.