Year	Percent
1970	14.34067
1971	15.87019
1972	20.42803
1973	19.22155
1974	21.53349
1975	22.76866
1976	22.48057
1977	24.53065
1978	28.06604
1979	28.22408
1980	31.66914
1981	32.42082
1982	35.33622
1983	51.72317
1984	52.93823
1985	49.35627
1986	42.80108
1987	42.57793
1988	37.21558
1989	25.62493
1990	26.75549
1991	20.58823
1992	32.95725
1993	33.85293
1994	28.46723
1995	21.23933
1996	21.96856
1997	23.27202
1998	29.31409
1999	43.14808
2000	38.68496
2001	43.04449
2002	47.67605
2003	44.13219
2004	34.28159
2005	21.98613
2006	18.29017
2007	17.81198
2008	16.28855
2009	17.73466
2010	16.43472
2011	15.85704
2012	18.25699
2013	19.80194
2014	23.13391
2015	30.79184
2016	30.89275