Year	Percent
1968-01-01	35.0484326053731
1969-01-01	35.1448231075682
1970-01-01	35.7883564734799
1971-01-01	35.4571573454304
1972-01-01	36.7340561823481
1973-01-01	36.1768267438327
1974-01-01	36.8951222961900
1975-01-01	37.1829348819950
1976-01-01	37.0841282551595
1977-01-01	37.5795707459539
1978-01-01	37.0365754937544
1979-01-01	36.8193656543482
1980-01-01	36.6992408029817
1981-01-01	37.0839738614071
1982-01-01	36.7949844843779
1983-01-01	36.0989268900518
1984-01-01	36.8944660086823
1985-01-01	36.8105401624938
1986-01-01	37.0442956654216
1987-01-01	36.7926106881176
1988-01-01	36.7767395770524
1989-01-01	36.0556817451035
1990-01-01	35.0698972792041
1991-01-01	33.7888596318667
1992-01-01	33.6355167744142
1993-01-01	33.4623704900329
1994-01-01	33.8621408318913
1995-01-01	33.7462767198931
1996-01-01	33.5662747809689
1997-01-01	33.1172474731740
1998-01-01	32.9092645713270
1999-01-01	32.8294133520087
2000-01-01	33.5077023288071
2001-01-01	34.1959841132960
2002-01-01	34.4694975574314
2003-01-01	34.1004831397260
2004-01-01	33.9084344576396
2005-01-01	33.3957963252174
2006-01-01	32.6501034060865
2007-01-01	31.4979368661427
2008-01-01	31.0321913415551
2009-01-01	31.0600369748518
2010-01-01	31.0856295407246
2011-01-01	31.0383711729366
2012-01-01	31.7016864437211
2013-01-01	30.4489191297234
2014-01-01	28.9587891485268
2015-01-01	27.5930954094146
2016-01-01	26.3041136684992
2017-01-01	24.5816681725217