They analyzed the Morningstar sustainability ratings of more than 20,000 mutual funds representing over $8 trillion in assets and concluded, "We do not find evidence that high-sustainability funds outperform low-sustainability funds." A study from Columbia had similar findings, but also flags other concerns, including that the companies held in ESG portfolios have "worse track records for compliance with labor and environmental laws" compared to companies held in non-ESG funds. However, if corporate governance criteria are singled out, well-governed companies perform better than those poorly run. The impact ESG funds have is also up in the air. The former head of sustainable investing at BlackRock, the world's largest asset manager, bluntly said, "The major problem that I have is that even if they're marketed correctly, they actually have no demonstrable impact."