Year	Percent
1974	8.14922
1975	9.14669
1976	8.42126
1977	14.21406
1978	18.30495
1979	14.89397
1980	14.54101
1981	17.45894
1982	19.46743
1983	21.70017
1984	25.46322
1985	26.97651
1986	39.26708
1987	38.56126
1988	45.51969
1989	39.23576
1990	37.47552
1991	39.40522
1992	38.63571
1993	41.68753
1994	44.97292
1995	44.56746
1996	42.57376
1997	42.72731
1998	47.05587
1999	43.58043
2000	35.30581
2001	38.82299
2002	38.24441
2003	34.63026
2004	31.01938
2005	27.49307
2006	26.11737
2007	28.00553
2008	25.25113
2009	33.68586
2010	30.60995
2011	25.75205
2012	26.69411
2013	29.29016
2014	31.43522
2015	37.53516
2016	42.97604
2017	40.85108