Year	Percent
1990	20.54
1991	20.253
1992	19.993
1993	19.673
1994	19.569
1995	19.6
1996	19.801
1997	20.004
1998	20.209
1999	20.415
2000	20.622
2001	20.831
2002	21.042
2003	21.254
2004	21.468
2005	21.683
2006	21.9
2007	21.181
2008	20.479
2009	19.794
2010	19.127
2011	18.477
2012	17.844
2013	17.229
2014	16.63
2015	16.824
2016	17.039
2017	16.855
2018	16.672
2019	16.489
2020	16.306
2021	16.123
2022	15.94
2023	15.757
2024	15.573
2025	15.39
2026	15.207
2027	15.024
2028	14.841
2029	14.658
2030	14.475