Year	Percent
1960	2.49999
1961	2.5222
1962	2.54776
1963	2.58861
1964	2.64953
1965	2.71921
1966	2.7931
1967	2.84971
1968	2.86943
1969	2.84445
1970	2.79241
1971	2.72579
1972	2.67403
1973	2.65892
1974	2.69146
1975	2.75073
1976	2.82728
1977	2.88047
1978	2.87448
1979	2.79464
1980	2.67446
1981	2.55462
1982	2.47605
1983	2.45027
1984	2.4915
1985	2.58288
1986	2.64961
1987	2.71331
1988	2.85865
1989	3.0993
1990	3.37617
1991	3.68752
1992	3.90796
1993	3.9056
1994	3.6413
1995	3.22992
1996	2.78518
1997	2.44722
1998	2.27906
1999	2.33237
2000	2.53355
2001	2.76113
2002	2.93499
2003	3.07115
2004	3.14931
2005	3.1867
2006	3.21973
2007	3.2615
2008	3.29355
2009	3.31644
2010	3.33094
2011	3.3383
2012	3.33887
2013	3.33237
2014	3.31918
2015	3.30042
2016	3.27853
2017	3.25353