Year	Percent
1961	2.57974
1962	2.51645
1963	2.50138
1964	2.51745
1965	2.68421
1966	2.79271
1967	2.8138
1968	2.8138
1969	2.84796
1970	2.85599
1971	2.86504
1972	2.86805
1973	2.86805
1974	2.85599
1975	2.83791
1976	2.74248
1977	2.64704
1978	2.55161
1979	2.45818
1980	2.45618
1981	2.47928
1982	2.45642
1983	2.44587
1984	2.4695
1985	2.50841
1986	2.57873
1987	2.55864
1988	2.5928
1989	2.58275
1990	2.6601
1991	2.65508
1992	3.00998
1993	3.02896
1994	3.02643
1995	3.29801
1996	3.19098
1997	3.25975
1998	3.27452
1999	3.49892
2000	3.30604
2001	3.35326
2002	3.43965
2003	3.42458
2004	3.4939
2005	3.5391
2006	3.54915
2007	3.55417
2008	3.55819
2009	3.70586
2010	3.68778
2011	3.63655
2012	3.71289
2013	3.74802
2014	3.73217
2015	3.8072
2016	3.75083
2017	3.85451
2018	3.88066
2019	3.93993
2020	3.98915
2021	4.04942