Year	Percent
1977	52.77077
1978	60.18914
1979	57.76234
1980	56.63643
1981	51.16609
1982	51.19399
1983	51.4141
1984	50.29041
1985	50.55778
1986	49.46279
1987	48.76546
1988	47.91198
1989	49.10149
1990	50.93786
1991	53.36844
1992	54.60497
1993	61.79423
1994	62.8004
1996	72.78513
1999	93.66732
2000	94.59839
2001	96.64646
2002	96.56456
2003	96.50002
2004	97.5885
2005	95.29373
2006	92.30752
2007	91.94805
2008	93.12642
2009	94.18436
2010	94.35484
2011	95.21214
2012	95.85163
2013	96.07933
2014	94.55129
2015	94.35872
2016	95.81337