An interesting presentation by Richard Wilkinson on material drawn the book The Spirit Level which he co-authored with Kate Pickett. Lots of good stuff about the link between a relative measure of inequality (the ratio of top to bottom incomes) and various measures of health, happiness, well being and social cohesion in developed economies. And since you asked the more unequal by this measure a society is the greater the problems and measures of the problems. Oh, possibly suicide may be a problem that runs counter to this. Good empirical stuff. See the Equality Trust and its publications. As you can imagine, lots of people want to pick a fight over it. Well they would. wouldn't they.
Heard a bit about tick boxes recently in connection with tax matters. Wilkinson had a nice idea to put forward. A tick box, optional, on tax returns to indicate people and companies would allow information to become a matter of public record. Nice one. We could start, of course, with the disclosure as a matter of public record, the ratio of tax paid to income. Voluntary, to begin with and qualifications in full, 'my dog ate the major part of my income last year'!