Year	Percent
1987	42.67744
1988	42.14572
1989	44.05177
1990	44.19261
1991	44.8199
1992	45.66468
1993	47.96711
1994	47.94434
1995	47.88243
1996	47.90073
1997	48.24358
1998	48.97085
1999	47.88241
2000	46.3015
2001	49.17309
2002	48.69654
2003	46.71024
2004	44.5475
2005	44.19734
2006	43.92635
2007	44.52025
2008	43.94816
2009	48.83603
2010	48.47742
2011	47.76684
2012	49.0224
2013	49.94463
2014	50.1226
2015	51.1707
2016	51.6639
2017	50.96257