One year ago, the U.S. had the 10th best retirement-income system in the world. One year later, that hasn't changed, according to the third annual study of the pension systems of 16 countries by Mercer and the Australian Centre for Financial Studies. In its study, Mercer and ACFS measured the overall pension benefits that are being provided to the citizens of 16 countries, the likelihood that those systems will be able to provide benefits in the future, and the integrity of private retirement plans. Same as last year, the U.S. didn't get such high marks. In fact, the U.S. earned a "C" grade for its pension-plan system according to the 2011 Melbourne Mercer Global Pension Index, the same grade awarded to Poland and Brazil. Read the Global Pension report here. The Netherlands and Australia earned the highest grades, a B+, for their respective retirement-income systems. Read my column from last year on the Melbourne Mercer index. By its own admission, Mercer and ACFS said comparing diverse retirement-income systems around the world is not easy. "Retirement-income systems are diverse and often a number of different programs," according to a report published by the Organization for Economic Cooperation and Development in March 2011. Classifying pension systems and different retirement-income schemes is consequentially difficult. At the moment, no country has a gold-standard pension system according to the Melbourne Mercer index. To receive a best-in-class grade, the researchers said a system would have to provide adequate retirement benefits, be sustainable over the longer term and be trusted due to its strong and robust governing structures. For his part, Nevin Adams, the director of education and external relations at the Employee Benefit Research Institute and the co-director of EBRI's Center for Research on Retirement Income, suggested that Americans should view the rankings with a large grain of salt.