Tanner invested $1,000 in large U.S. stocks at the beginning of 2012. This investment earned 15.98 percent in 2012, 31.66 percent in 2013, 13.69 percent in 2014, and 1.41 percent in 2015. What return did he earn in the average year during the 2012 to 2015 period? Round answer to 4 decimal places present percentage as a decimal.