Year	Percent
1971	94.30488
1972	93.04782
1973	92.21012
1974	95.40393
1975	97.12287
1976	100.57151
1977	100.40017
1978	98.47723
1979	96.86467
1980	96.06841
1981	94.36728
1982	94.06056
1983	94.93168
1984	93.85126
1985	95.84606
1986	97.16873
1987	98.78221
1988	100.09891
1989	100.91916
1990	97.82297
1991	96.13199
1992	97.17109
1993	99.2503
1994	95.6775
1995	95.2014
1996	98.00289
1997	99.14728
1998	97.39181
1999	96.58648
2000	95.70695
2001	97.54382
2002	97.13737
2003	97.95063
2004	98.02671
2005	94.6327
2006	93.3957
2007	93.15292
2009	92.92282
2010	93.53063
2011	93.64822
2012	94.41447
2013	96.08846
2014	96.0194
2015	98.75548
2016	100.16309