This is the problem with using a relative measure rather than an absolute. There can only ever be 20% of people in each relative quintile, but the percentage of

This is the problem with using a relative measure rather than an absolute. There can only ever be 20% of people in each relative quintile, but the percentage of the population above and below a given wealth line can change dramatically. If through some social magic, everyone was elevated above the poverty line, you'd still have a lowest quintile.