Year	Percent
1990	39.4
1991	38.15
1992	39.66
1993	39.58
1994	38.6
1995	39.65
1996	40.71
1997	41.62
1998	42.38
1999	41.14
2000	42.45
2001	40.6
2002	38.35
2003	39.74
2004	40.53
2005	37.15
2006	36.86
2007	39.91
2008	40.18
2009	40.48
2010	40.46
2011	38.84
2012	38.94
2013	38.56
2014	39.03
2015	39.52
2016	39.47
2017	41.01
2018	42.02
2019	43.49