Inequity and inequality are closely related in origin and in some of their secondary definitions, so mixing them up is never a serious error, but there are differences between them. Inequality refers primarily to the condition of being unequal, and it tends to relate to things that can be expressed in numbers.1 Inequity, in its main sense, is a close synonym of injustice and unfairness, so it usually relates to more qualitative matters.2 For example, one might say that income inequality results from inequity in society, or that inequality in taxation is a great inequity.
But inequality does cross into more qualitative territory in some of its secondary uses, especially where it refers to a lack of equality in opportunity or treatment. Inequality in this sense, often used in reference to disparities in rights or freedoms, is virtually interchangeable with inequity. Because the words come so close together here, the use of inequality in place of inequity is rarely a problem. Using inequity in place of inequality in the latter’s quantitative senses is potentially problematic, however, because inequity is not conventionally used this way.
Except where it refers to lack of equality in opportunity or treatment, inequality usually describes measurable disparities—for example:
The U.S. has a higher level of income inequality than Europe, as well as Canada, Australia and South Korea. [CNN Money]
Inequality between countries in access to food, water, housing and work will only increase. [Guardian]
[I]f we win the election we will set up a fair pay review to investigate pay inequality in the public sector. [quoted in The Age]
And inequity describes not-so-measurable disparities—for example:
Aboriginal children in Canada are in crisis, facing gross inequities and lacking opportunities open to other Canadian children. [Vancouver Sun]
Clinton had listened as speaker after speaker used the occasion of her death for sermons on civil rights and racial inequity. [New York Times]
If allowed, it merely reinforces the all too common notion of the inequity of our justice system. [letter to Houston Chronicle]