Year	Percent
1990	33.914
1991	33.458
1992	33.006
1993	33.033
1994	32.86
1995	34.305
1996	35.779
1997	37.281
1998	38.016
1999	38.756
2000	39.501
2001	39.304
2002	39.108
2003	38.912
2004	38.716
2005	38.521
2006	38.326
2007	38.131
2008	37.937
2009	37.743
2010	37.55
2011	37.357
2012	37.164
2013	36.972
2014	36.78
2015	36.357
2016	36.402
2017	36.244
2018	36.087
2019	35.929
2020	35.772
2021	35.614
2022	35.456
2023	35.299
2024	35.141
2025	34.983
2026	34.826
2027	34.668
2028	34.511
2029	34.353
2030	34.195