Year	Percent
1991	40.359
1992	39.784
1993	39.167
1994	38.758
1995	38.841
1996	38.539
1997	38.688
1998	39.075
1999	39.46
2000	39.54
2001	39.994
2002	40.012
2003	39.936
2004	39.346
2005	39.205
2006	38.196
2007	37.005
2008	38.627
2009	38.902
2010	36.578
2011	34.984
2012	35.18
2013	35.268
2014	35.256
2015	35.546
2016	36.711
2017	36.934
2018	37.421
2019	38.001
2020	38.586
2021	39.14
2022	39.704