Year	Percent
1980	51.94297
1981	49.21259
1982	53.83916
1983	53.6827
1984	55.53568
1985	50.05833
1986	41.4928
1987	42.50021
1988	41.77131
1989	39.28892
1990	37.14634
1991	38.20767
1992	41.85046
1993	37.71171
1994	47.24826
1995	44.56642
1996	41.38095
1997	43.02393
1998	37.25696
1999	33.91353
2000	28.11037
2001	29.52323
2002	28.16421
2003	31.86839
2004	32.46325
2005	36.38055
2006	38.3312
2007	41.37728
2008	48.80684
2009	48.38572
2010	51.67938
2011	52.23687
2012	56.31738
2013	59.85169
2014	60.29883
2015	47.28516
2016	43.74482
2017	44.2