Year	Percent
1971	0.40172
1981	0.46379
1982	0.45913
1983	0.44871
1984	0.44868
1985	0.43115
1986	0.43249
1987	0.41449
1989	0.41574
1990	0.41923
1991	0.42915
1993	0.43429
1994	0.4512
1996	0.48776
1999	0.56189
2001	0.62488
2002	0.6477
2003	0.67717
2004	0.6885
2005	0.712
2006	0.73094
2008	0.75699
2011	0.78175
2014	0.78774