I haven't. Any use of a particular portion of the distribution of income would be a relative measure, regardless of where it's set. There is a variety of them out there. Typically they would be a percentage of median income—that's what's used in Europe—typically 60% of median after-tax income.
The research I've done is typically on market basket types of measures, looking at the measurement of basic needs and the number of people who are unable to afford that, and trying to use comparisons with other nations.