Investing in private equity funds is barely worth it, said a National Bureau of Economic Research study.

Just this month, NBER published the working paper "Valuing Private Equity" authored by Columbia business school associate professor Morten Sorensen. The working paper is currently being reviewed by Columbia and Shanghai University of Finance and Economics academics Neng Wang and Jinqiang Yang.

The group analyzed limited partnership portfolios and found that private equity investors essentially only break even when illiquidity, risk of losing money and other costs are taken into account.

According to the research, private equity firms such as Blackstone Group, KKR & Co. or Carlyle Group must generate a so-called public market equivalent of about 1.30 on average to break even.

The number compares PE fund returns to an index like the Standard & Poor's 500. A figure greater than 1 signifies that the PE fund outperformed. The average return for PE funds is 1.27, said a CNBC report.