Year	Percent
1971	31.81979
1972	31.19499
1973	35.21221
1974	43.4455
1975	38.28111
1976	37.31017
1977	45.20175
1978	42.70399
1979	47.32
1980	48.58168
1981	50.72043
1982	52.97956
1983	49.3222
1984	47.72839
1985	51.96706
1986	52.57505
1987	50.22975
1988	52.87996
1989	58.07601
1990	63.08146
1991	66.042
1992	60.78816
1993	53.60071
1994	54.80538
1995	55.83304
1996	50.60427
1997	49.69552
1998	55.97137
1999	60.34093
2000	62.34129
2001	67.7675
2002	65.86148
2003	73.73676
2004	68.57397
2005	67.3819
2006	68.8833
2007	67.0331
2008	68.29781
2009	63.08678
2010	62.67169
2011	64.64865
2012	58.00642
2013	60.90473
2014	60.96609
2015	67.27608
2016	68.4119