At last year’s World Economic Forum in Davos, Switzerland, the head of Goldman Sachs announced a new policy for the richest investment bank in the world: It would refuse to underwrite the stock offerings of any private company that did not have at least one woman on its board of directors—and that the minimum would move up to two in 2022. “This decision is rooted first and foremost in our conviction that companies with diverse leadership perform better,” the Goldman CEO, David Solomon, declared. “Companies that have gone public with at least one female board director outperformed companies that do not.” Solomon gave no source for this assertion, and Goldman did not reply to a request for comment. But much of the authority for claims like his rest on three studies done between 2015 and 2020 by the consulting company McKinsey, which were trumpeted as proof that large companies can …