Year	Percent
1960	6.46267
1961	6.30448
1962	6.1417
1963	5.64313
1964	5.40522
1965	5.23268
1966	5.10742
1967	5.11354
1968	4.92496
1969	4.38079
1970	4.11745
1971	3.94785
1972	3.84571
1973	3.74263
1974	3.67444
1975	3.80624
1976	3.75742
1977	3.84722
1978	3.75188
1979	3.73749
1980	3.75631
1981	3.86456
1982	3.83802
1983	3.85384
1984	3.7946
1985	3.74289
1986	3.67364
1987	3.71493
1988	3.5277
1989	3.4286
1990	3.3397
1991	3.34788
1992	3.20326
1993	3.20192
1994	3.16721
1995	2.96735
1996	2.87446
1997	2.82795
1998	2.65033
1999	2.59275
2000	2.47101
2001	2.4075
2002	2.42627
2003	2.48461
2004	2.49538
2005	2.40099
2006	2.34489
2007	2.27546
2008	2.25784
2009	2.48301
2010	2.33417
2011	2.25666
2012	2.23894
2013	2.22243
2014	2.2326
2015	2.27422
2016	2.32702
2017	2.25523