A new study shows that combining ESG factors with high employee satisfaction leads to outperformance, according to a recent article in Institutional Investor.

The study used data from employee-rating site Glassdoor and MSCI’s ESG ratings to build portfolios using both scores. The report—published last month by Kyle Welch of George Washington University and Aaron Yoon of Northwestern University—shows that portfolios with high ESG ratings and high employee satisfaction outperform those with low ratings by nearly 6 percent.

Yoon explained, “We know that employee satisfaction is related to firm value and enhancing stock returns. Before doing this work, we didn’t know what the role of ESG is in shaping that relationship.” He added, “Employees are so very important. They’re not just raw materials.”