This is from Mauboussin’s article on calculating ROIC
An adjustment for minority interest is relevant either when another company owns a meaningful minority percentage of the company you are analyzing or the company you are analyzing owns a meaningful minority stake in another company. In the first case, the best course is to calculate ROIC as if the business is wholly owned. In fact, this takes little additional analysis since minority interest falls below the EBITA line—you just need to watch taxes. The minority stake is relevant for valuation, of course. You need to subtract the value of the minority stake in order to correctly calculate shareholder value per share.
How is a minority stake different from any stock owned by any other retail investor in the company? A minority stake would essentially mean some other company owning a percentage of the stock in the company or is it something else? If so, why is any adjustment necessary?