A study released Wednesday by Natixis Global Asset Management illustrates what U.S. investors already knew: last year was lousy for long-only investors.

According to Natixis, U.S. portfolios lost an average of 0.9% in 2015. That ranked last from among 855 model portfolios in the moderate risk category Natixis analyzed from financial advisors and other investment professionals in France, Italy, Latin America, Singapore, Spain, the United Kingdom and the United States.

The study was done by Natixis Portfolio Clarity, the company’s portfolio consulting service. While not an all-encompassing look at the global investing scene, it nonetheless puts some perspective on the pain U.S. investors felt last year.

French portfolios scored best with average gains of 7.6 percent. Natixis, which has $870 billion in assets under management, has headquarters in Paris and Boston.

Natixis says the performance gap between eight major asset classes in the U.S. hit a 10-year low last year, with the top-performing asset class, municipal bonds, up just 3.3 percent. In other words, the tight range meant U.S. investors who stuck with domestic markets were doomed to mediocrity.

The top 10 percent of U.S. portfolios outperformed the bottom 10 percent by six percentage points, and the best-performing U.S. portfolios shared several commonalities: higher exposure to large-cap stocks and growth stocks, lower exposure to emerging markets and better manager selection.

Growth outperformed value by 9.5 percentage points in 2015, according to Natixis. Meanwhile, a strong dollar dented returns on overseas investments.

Natixis found that U.S. portfolios held 54 percent of assets in stocks, 28 percent in bonds, 7 percent in asset allocation funds that are a mix of asset categories, and 7 percent in alternative strategies such as managed futures, global macro, and long-short funds. The remaining assets were in money market funds, real estate investment trusts and commodities.

Natixis says the tendency toward home bias among investors, coupled with disparities in performance across international financial markets and regional differences in portfolio construction, led to the variation between global portfolios in the study.

French investors, for example, got a boost from higher allocations to outperforming European equities and a preference for risk-managed investments.