Year	Percent
1974	17.35341
1975	23.42622
1976	18.25887
1977	16.08782
1978	14.47273
1979	14.13787
1980	11.66427
1981	13.71348
1982	17.22645
1983	18.98103
1989	35.20789
1990	37.26689
1991	40.17201
1992	47.90902
1993	51.76364
1994	48.40621
1995	55.82712
1996	60.64051
1997	58.49423
1998	57.40413
1999	48.40323
2000	35.81729
2001	39.19356
2002	41.62614
2003	35.96922
2004	31.79052
2005	27.28917
2006	25.21645
2007	27.89772
2008	27.61461
2009	35.78946
2010	27.96148
2011	30.03047
2012	35.47872
2013	42.895
2014	30.65049
2015	32.68647
2016	37.74202
2017	35.60355