Year	Percent
1991	39.82182
1992	39.89745
1993	40.20642
1994	40.08467
1995	39.5503
1996	38.97306
1997	38.54075
1998	38.15331
1999	37.85883
2000	37.4967
2001	37.21363
2002	36.55373
2003	36.44641
2004	36.16357
2005	38.10669
2006	40.21176
2007	42.21529
2008	44.37262
2009	46.5076
2010	48.87846
2011	51.218
2012	51.22677
2013	51.18637
2014	51.14285
2015	51.15273
2016	51.15475
2017	50.99549
2018	50.91032
2019	50.73223