Year	Percent
1960	10.74993
1961	11.00393
1962	11.48195
1963	11.97931
1964	12.47611
1965	12.96653
1966	13.25143
1967	13.34044
1968	13.45792
1969	13.55679
1970	13.62519
1971	12.75827
1972	12.66269
1973	12.58349
1974	12.48998
1975	12.3839
1976	12.28276
1977	12.18364
1978	12.09299
1979	12.01176
1980	11.93282
1981	11.92151
1982	11.97529
1983	12.03074
1984	12.08102
1985	12.12233
1986	12.15567
1987	12.17679
1988	12.18267
1989	12.16313
1990	12.13089
1991	12.19871
1992	12.36963
1993	12.54298
1994	12.70258
1995	12.88817
1996	13.06556
1997	13.19857
1998	13.33338
1999	13.46653
2000	13.58998
2001	13.67036
2002	13.71432
2003	13.752
2004	13.78699
2005	13.8209
2006	13.91497
2007	14.06845
2008	14.21865
2009	14.35925
2010	14.50153
2011	14.66414
2012	14.83601
2013	14.99295
2014	15.13002
2015	15.25839
2016	15.35765
2017	15.42729