Year	Percent
1960	38.73261
1961	38.84657
1962	39.01326
1963	39.22418
1964	39.46198
1965	39.7592
1966	40.10306
1967	40.48186
1968	40.90775
1969	41.35012
1970	41.59434
1971	41.41047
1972	41.31589
1973	41.27658
1974	41.26292
1975	41.22788
1976	41.21674
1977	41.1904
1978	41.15138
1979	41.10335
1980	41.13373
1981	41.18912
1982	41.26203
1983	41.35648
1984	41.47732
1985	41.59418
1986	41.7017
1987	41.82778
1988	41.95467
1989	42.07098
1990	42.14996
1991	42.24918
1992	42.33276
1993	42.44831
1994	42.60932
1995	42.7911
1996	42.9915
1997	43.17863
1998	43.38952
1999	43.61453
2000	43.79138
2001	43.80948
2002	43.8599
2003	43.94498
2004	44.00648
2005	44.07314
2006	44.12658
2007	44.19076
2008	44.26294
2009	44.36957
2010	44.50151
2011	44.67946
2012	44.86038
2013	45.0638
2014	45.2557
2015	45.45234
2016	45.66602
2017	45.89633