Year	Percent
1990	45.12
1991	45.58
1992	45.97
1993	46.41
1994	46.69
1995	47.3
1996	47.65
1997	47.97
1998	48.29
1999	48.61
2000	47.64
2001	46.72
2002	45.86
2003	45.04
2004	44.26
2005	43.52
2006	42.84
2007	42.2
2008	41.6
2009	41.08
2010	40.63
2011	39.82
2012	39.13
2013	38.52
2014	37.96
2015	38.39
2016	38.7
2017	38.97
2018	39.19
2019	39.39