Year	Percent
1990	81.807
1991	81.846
1992	81.831
1993	81.684
1994	81.605
1995	81.417
1996	81.457
1997	81.622
1998	81.755
1999	81.796
2000	81.871
2001	81.852
2002	81.685
2003	81.901
2004	82.097
2005	81.885
2006	81.967
2007	81.578
2008	81.166
2009	81.191
2010	80.802
2011	81.199
2012	81.026
2013	80.84
2014	80.158
2015	80.177
2016	80.214
2017	80.176
2018	80.125
2019	80.074
2020	80.032
2021	79.996
2022	79.968
2023	79.944
2024	79.916
2025	79.881
2026	79.838
2027	79.791
2028	79.741
2029	79.692
2030	79.646