Year	Percent
1981	19.41
1982	19.4
1987	16.71
1989	18.29
1990	29.81
1991	32.99
1998	23.23
2000	22.49
2002	19.99
2003	23.64
2004	20.17
2006	22.81
2010	21.91
2011	19.85
2012	19.5
2013	18.16
2014	19.46
2015	18.89
2016	21.01