Year	Percent
1980	30.76783
1981	42.00508
1982	49.49129
1983	47.52525
1984	46.51603
1985	45.41854
1986	35.07956
1987	32.58097
1988	35.66668
1989	30.69442
1990	27.99656
1991	33.22213
1992	34.18597
1993	30.73209
1994	34.45272
1995	31.91083
1996	27.39313
1997	28.58468
1998	27.85592
1999	28.75365
2000	27.96223
2001	30.89592
2002	29.18079
2003	30.45072
2004	28.31345
2005	29.10644
2006	30.81811
2007	32.89498
2008	35.58229
2009	43.00541
2010	47.77175
2011	51.60044
2012	51.30574
2013	49.30268
2014	46.58385
2015	40.74998
2016	40.53624
2017	41.47924