Year	Percent
1990	17.94
1991	18.188
1992	18.413
1993	18.631
1994	18.824
1995	19.002
1996	19.108
1997	19.016
1998	18.779
1999	18.868
2000	18.951
2001	19.007
2002	19.121
2003	19.249
2004	19.351
2005	19.412
2006	19.485
2007	19.559
2008	19.58
2009	19.568
2010	19.067
2011	19.8
2012	19.93
2013	19
2014	18.9
2015	17.83
2016	17.844
2017	17.87
2018	17.896
2019	17.922
2020	17.948
2021	17.974
2022	18
2023	18.026
2024	18.052
2025	18.078
2026	18.104
2027	18.13
2028	18.156
2029	18.182
2030	18.208