Year	Percent
1991	19.198
1992	19.034
1993	18.889
1994	18.786
1995	18.539
1996	18.188
1997	17.855
1998	17.516
1999	17.204
2000	16.995
2001	16.675
2002	16.499
2003	16.406
2004	16.354
2005	16.309
2006	16.266
2007	16.23
2008	16.204
2009	16.225
2010	16.359
2011	16.416
2012	16.568
2013	16.779
2014	17.001
2015	17.207
2016	17.342
2017	17.377
2018	17.413
2019	17.45
2020	17.484
2021	17.513
2022	17.541