Year	Percent
1991	42.339
1992	42.664
1993	42.973
1994	44.896
1995	42.943
1996	39.995
1997	33.156
1998	30.209
1999	27.792
2000	25.052
2001	24.681
2002	23.848
2003	22.995
2004	23.166
2005	21.909
2006	21.459
2007	20.417
2008	19.656
2009	18.669
2010	18.468
2011	18.256
2012	18.229
2013	18.109
2014	16.812
2015	18.69
2016	19.537
2017	19.382
2018	18.825
2019	18.336
2020	17.883
2021	17.418
2022	16.987