Year	Percent
1991	18.251
1992	18.348
1993	18.399
1994	18.518
1995	18.766
1996	19.063
1997	19.324
1998	19.339
1999	19.379
2000	19.48
2001	19.638
2002	19.701
2003	19.804
2004	19.17
2005	20.257
2006	20.711
2007	21.177
2008	21.145
2009	19.81
2010	19.826
2011	17.756
2012	18.77
2013	19.292
2014	19.522
2015	19.118
2016	18.663
2017	18.647
2018	18.617
2019	18.561
2020	18.482
2021	18.389
2022	18.276