Year	Percent
1990	20.181
1991	20.239
1992	20.229
1993	20.243
1994	20.241
1995	20.229
1996	20.204
1997	20.177
1998	20.126
1999	19.992
2000	19.889
2001	19.797
2002	19.679
2003	19.569
2004	19.452
2005	19.36
2006	19.189
2007	19.079
2008	18.936
2009	18.823
2010	18.756
2011	18.706
2012	18.649
2013	18.597
2014	18.542
2015	18.485
2016	18.511
2017	18.416
2018	18.32
2019	18.225
2020	18.13
2021	18.034
2022	17.939
2023	17.843
2024	17.748
2025	17.652
2026	17.557
2027	17.462
2028	17.366
2029	17.271
2030	17.175