Doing Business introduces 3 new measures of minority investor protections this year—indices on shareholders’ rights and role in major corporate decisions, on governance structure and on corporate transparency.

http://www.doingbusiness.org/~/media/GIAWB/Doing%20Business/Documents/Annual-Reports/English/DB15-Chapters/DB15-CaseStudy-Protecting-Minority-Investors.pdf

As a lawyer, the first place to look is always company law - pretty much every company statute I have seen contains minority shareholder rights. Once you know that, you can start to look at measuring their value to minority shareholders. In my experience however listed companies do not need to bother because minority shareholders can sell easily. It is in the SME sector that such rights have more value, particularly in relation to valuation of shares when a minority shareholder wants out. The other place such rights are found are shareholder agreements, again common only in the SME sector.

Well beyond a big mass of studies on ssrn.com if you wanna try something new

I think you should use Hirsch's positional goods

Decisions independent or transfered to banks or other entities.Informations  given to   shareholder, their transparency. Structure of shareholders.

in millimetres