Stocks and bonds have gotten a little too close for some institutional investors’ comfort, according to a recent study from Boston-based Natixis Global Asset Managment.

According to the Natixis Global Asset Management Institutional Investor study, more than half of institutional investors, 54 percent, report difficulty in finding diversification among traditional asset classes because stocks and bonds are too highly correlated to provide distinctive sources of return.

Increasing correlation is occurring at a moment when institutional investors are prospecting for alpha — most institutional investors, 87 percent, believe that active management is a source of alpha. A recent BlackRock study also found growing interest in alternatives by institutional investors.

Natixis’s research showed that investors want advice and products that help them manage liability and longevity risks, 68 percent of respondents said that it is a challenge to manage uncertain liabilities linked to longevity.

That desire could be pushing more institutional investors toward alternatives. Two-thirds, 66 percent, of respondents believe that increasing allocations to non-correlated assets would be an effective way to reduce risk, and almost half, 49 percent, believe it is essential to invest in alternatives in order to outperform the broader markets.

Investors were also concerned about the low-yield environment, according to the survey, with 84 percent of respondents naming yield as their biggest concern for managing risk. Investors also mentioned generating returns, 82 percent, and funding long-term liabilities, 74 percent, as concerns. Many institutional investors, 68 percent, also reported being challenged by meeting growth objectives and short-term liquidity needs.

The intersecting concerns may be driving institutional investors back toward favoring active management; currently, 64 percent of respondents’ assets are managed actively. Most respondents, 77 percent, believe active management is better for accessing non-correlated asset classes, and 58 percent told Natixis that active investments will outperform passive ones over the long term. In the short term, 67 percent of respondents say conditions like economic factors and monetary policies will be favorable for active management over the next 12 months.

In their search for alpha, institutional investors are screening for different factors when selecting investments, including environmental, social and governance (ESG) factors. Almost all of the investors surveyed, 95 percent, are incorporating ESG strategies in their portfolios to some extent, and 50 percent see ESG factors as a potential source of return, while 51 percent believe ESG assessments can mitigate some risks. Another 31 percent of respondents are incorporating ESG because it is in their fund’s mandate.

For the study, Natixis surveyed 660 institutional investors, including corporate, public and government pension funds; sovereign wealth funds; insurance companies; endowments and foundations collectively managing more than $35 trillion in assets.