Year	Percent
1972	28.9961
1973	28.23529
1974	28.07676
1975	26.68958
1976	26.02644
1999	27.67062
2000	31.49446
2001	31.34118
2005	38.03405
2006	42.19515
2008	47.66403
2011	47.71772
2013	50.8456
2014	59.89464
2015	64.45043
2016	65.80619
2017	60.26019