Year	Percent
1991	67.971
1992	68.755
1993	68.582
1994	68.155
1995	67.137
1996	66.284
1997	65.273
1998	63.826
1999	62.576
2000	61.559
2001	59.805
2002	58.236
2003	56.76
2004	55.383
2005	54.632
2006	53.821
2007	53.89
2008	52.648
2009	52.326
2010	51.765
2011	50.61
2012	49.166
2013	47.492
2014	45.787
2015	44.191
2016	42.706
2017	42.055
2018	41.324
2019	40.625
2020	39.998
2021	39.442
2022	38.988