Year	%
1978	62.64978
1979	62.36803
1980	61.57463
1981	59.38309
1982	59.72231
1983	58.65181
1984	57.85525
1985	59.86534
1986	60.99776
1987	61.28092
1988	62.11796
1989	62.40154
1990	62.73975
1991	62.84157
1992	62.99769
1993	62.74074
1994	63.84141
1998	67.44813
1999	67.58313
2000	68.88726
2001	71.07727
2002	72.75851
2003	74.40421
2004	75.49314
2005	76.9664
2006	77.66626
2007	77.92554
2008	77.30531
2009	77.97439
2010	78.26439
2011	79.54973
2012	77.66498
2013	79.03277
2014	78.89812
2015	79.93312