Year	Percent
1960	2.9987
1961	3.18711
1962	3.35593
1963	3.46438
1964	3.49707
1965	3.49222
1966	3.48086
1967	3.51929
1968	3.64119
1969	3.86213
1970	4.14121
1971	4.43394
1972	4.68918
1973	4.88656
1974	5.01417
1975	5.10006
1976	5.11559
1977	5.14737
1978	5.30222
1979	5.59828
1980	5.93167
1981	6.22924
1982	6.36617
1983	6.27735
1984	5.94951
1985	5.48666
1986	5.02651
1987	4.62597
1988	4.24285
1989	3.88725
1990	3.55912
1991	3.25994
1992	2.98448
1993	2.72966
1994	2.49573
1995	2.29314
1996	2.09019
1997	1.93601
1998	1.91375
1999	2.05074
2000	2.28905
2001	2.564
2002	2.78989
2003	2.92453
2004	2.93768
2005	2.87182
2006	2.7749
2007	2.70639
2008	2.6888
2009	2.74044
2010	2.82594
2011	2.91896
2012	2.95999
2013	2.90756
2014	2.74138
2015	2.50414
2016	2.25142
2017	2.03193