Year	Percent
1972	27.29227
1973	28.59522
1974	34.49465
1975	35.76747
1976	33.82935
1977	30.25893
1978	29.39862
1979	29.6209
1980	28.91275
1981	30.74111
1982	31.33249
1983	33.64678
1984	35.46408
1985	35.86821
1986	35.81298
1987	37.01208
1988	39.22018
1989	40.31573
1990	41.57277
1991	41.92815
1992	44.95804
1993	45.50271
1994	48.26779
1995	53.64186
1996	53.07933
1997	52.75979
1998	53.67073
1999	54.67685
2000	52.80121
2001	55.39744
2002	55.66756
2003	57.65483
2004	58.5673
2005	52.70135
2006	66.38762
2007	63.88834
2008	62.207
2009	61.14929
2010	63.88996
2011	64.3995
2012	63.77794
2013	64.51859
2014	66.44363
2015	67.24067
2016	71.0682