Year	Percent
1991	54.775
1992	55.04
1993	55.375
1994	55.108
1995	54.213
1996	52.693
1997	50.641
1998	49.395
1999	47.542
2000	43.769
2001	42.114
2002	40.038
2003	37.412
2004	34.609
2005	31.412
2006	28.404
2007	24.262
2008	21.341
2009	18.598
2010	16.306
2011	15.804
2012	15.414
2013	15.222
2014	14.991
2015	15.007
2016	15.106
2017	15.189
2018	15.319
2019	15.349
2020	15.194
2021	14.896
2022	14.432