Since 1950, there have been 58 different 10-year periods (i.e., the 10-years from 1950-59, 1951-60, 1952-61 . . . , 2007-2016). The S&P 500 has produced a positive total return result in 56 of the 58 decade long periods, i.e., 97% of the time. (via BTN Research).