Year	Percent
1971	21.14286
1972	22.96888
1973	25.49926
1974	26.71138
1975	28.45436
1977	30.42516
1978	27.95298
1980	37.67644
1981	48.67354
1982	47.82209
1983	46.07371
1984	47.03479
1985	48.03043
1986	44.31268
1987	43.53422
1988	43.97272
1989	44.11912
1990	43.18279
1991	43.55448
1992	46.54128
1999	29.49534
2000	23.21242
2001	24.6675
2002	30.69867
2003	41.2709
2004	41.45892
2008	52.37143
2009	69.49379
2010	70.87532
2012	69.90703
2013	67.80348
2014	61.61636
2015	61.8355
2016	67.26458