Year	Percent
1991	18.83
1992	18.74
1993	18.578
1994	18.743
1995	18.617
1996	18.416
1997	18.351
1998	18.715
1999	18.739
2000	18.775
2001	18.979
2002	19.417
2003	19.541
2004	19.649
2005	19.72
2006	19.623
2007	19.613
2008	19.52
2009	19.511
2010	19.406
2011	19.123
2012	19.205
2013	19.276
2014	19.422
2015	19.318
2016	18.6
2017	18.781
2018	18.888
2019	18.989
2020	19.112
2021	19.255
2022	19.399