Year	Percent
1971	26.49723
1972	28.90993
1973	31.14279
1974	32.79917
1975	33.72705
1977	34.86205
1980	40.46669
1981	51.88438
1982	51.25883
1983	48.55107
1984	49.67533
1985	50.08345
1986	46.12468
1987	44.50789
1988	45.11435
1989	45.29815
1990	44.30268
1991	44.01111
1992	47.87806
1999	30.58204
2000	24.91291
2001	25.83652
2002	31.24754
2003	41.67034
2004	42.18899
2008	50.54306
2009	65.9933
2010	66.31336
2012	65.29898
2013	62.07351
2014	56.31476
2015	56.35285
2016	60.98356