Year	Percent
1960	30.705
1961	30.943
1962	31.015
1963	31.086
1964	31.158
1965	31.23
1966	31.302
1967	31.374
1968	31.446
1969	31.548
1970	31.74
1971	31.933
1972	32.127
1973	32.321
1974	32.516
1975	32.712
1976	32.908
1977	33.105
1978	33.302
1979	33.5
1980	33.762
1981	34.024
1982	34.287
1983	34.552
1984	34.817
1985	35.083
1986	35.35
1987	35.619
1988	35.888
1989	36.158
1990	36.428
1991	36.7
1992	37.249
1993	37.799
1994	38.354
1995	38.911
1996	39.473
1997	40.035
1998	40.601
1999	41.169
2000	41.741
2001	42.435
2002	43.501
2003	44.573
2004	45.651
2005	46.731
2006	47.815
2007	48.902
2008	49.991
2009	51.076
2010	52.163
2011	53.247
2012	54.33
2013	55.387
2014	56.423
2015	57.434
2016	58.421
2017	59.383