Year	Percent
1980	21.39979
1981	24.59964
1982	24.50012
1983	22.59985
1984	22.90006
1985	22.09986
1986	21.79988
1987	20.99982
1988	22.20014
1989	22.89974
1990	15.89841
1991	18.0078
1992	25.03757
1993	22.45732
1994	24.64834
1995	21.68991
1996	44.24277
1997	47.93125
1998	50.11539
1999	52.97256
2000	50.38873
2001	51.36966
2002	50.06
2003	46.30633
2004	46.18798
2005	46.93311
2006	46.26563
2007	47.21999
2008	44.69923
2009	45.31738
2010	44.02549
2011	44.25637
2012	44.95462
2013	44.607
2014	45.78252
2015	46.28433
2016	46.67473
2017	47.25967