Year	Percent
1980	45
1981	43.00006
1982	43.80017
1983	43.30005
1984	44
1985	43.30013
1986	44.20011
1987	45.80015
1988	46.29998
1989	44.80006
1990	48.2008
1991	42.69691
1992	23.32056
1993	22.90171
1994	21.73068
1995	22.49794
1996	14.38965
1997	14.19567
1998	11.64594
1999	12.56678
2000	14.81868
2001	16.43884
2002	17.4651
2003	20.45449
2004	21.63198
2005	22.10099
2006	22.88925
2007	21.83372
2008	25.16102
2009	24.41367
2010	24.93749
2011	24.48441
2012	22.91851
2013	23.06134
2014	21.50886
2015	21.76365
2016	21.13073
2017	21.14749