Year	Percent
1971	27.33168
1972	25.73757
1973	31.94162
1974	28.24358
1975	35.78132
1976	30.73302
1977	32.47463
1978	40.11842
1981	30.11982
1982	29.77952
1983	26.57859
1986	37.34767
1987	27.73554
1988	28.78207
1989	28.34105
1990	30.10823
1991	27.91326
1992	22.43461
2004	23.66221
2005	25.94951
2006	26.05538
2008	35.05311
2009	37.60859
2010	39.76394
2011	41.5809
2012	43.7301
2016	42.15803