Year	Percent
1960	6.69965
1961	7.69049
1962	8.61476
1963	8.95354
1964	9.3031
1965	9.66047
1966	10.02819
1967	10.40526
1968	10.79213
1969	11.18513
1970	11.58614
1971	11.99458
1972	12.4115
1973	12.83294
1974	13.32365
1975	13.91755
1976	14.54033
1977	15.19219
1978	15.86417
1979	16.53545
1980	17.19973
1981	17.83555
1982	18.47198
1983	19.18721
1984	20.67219
1985	23.44201
1986	26.88646
1987	31.1203
1988	36.28039
1989	42.43708
1990	49.67777
1991	58.24488
1992	46.76662
1993	37.30497
1994	29.23252
1995	22.37791
1996	38.16397
1997	34.16432
1998	30.43207
1999	27.354
2000	28.96605
2001	31.19294
2002	34.02196
2003	37.34669
2004	40.92666
2005	36.85821
2006	32.91994
2007	29.24799
2008	26.77758
2009	26.70026
2010	26.74566
2011	26.91914
2012	27.18854
2013	27.52011
2014	27.87416
2015	28.22087
2016	28.55569
2017	28.88849