Year	%
1971	65.23673
1972	63.14368
1973	60.82799
1974	60.76437
1975	60.29866
1976	60.39094
1977	61.01198
1978	61.25722
1979	61.29498
1980	61.34816
1981	57.51691
1982	58.8545
1983	59.13172
1984	58.83302
1985	61.24114
1986	61.62019
1987	62.8653
1988	63.12218
1989	62.92884
1990	63.31988
1991	64.04038
1992	64.54541
1993	64.96043
1994	66.47946
1995	67.75007
1996	69.29329
1997	69.90139
1998	72.43094
1999	72.57534
2000	73.71346
2001	75.13081
2002	76.51017
2003	78.64538
2004	81.05249
2005	81.72757
2006	82.93445
2007	83.26243
2008	81.25576
2009	82.04591
2010	82.49752
2011	83.1043
2012	81.80086
2013	82.24255
2014	82.1597
2015	82.94399
2016	81.92585
2017	81.36222