Year	Percent
1968-01-01	45.8827904895351
1969-01-01	46.3911340060886
1970-01-01	46.5430140576220
1971-01-01	47.4653823533183
1972-01-01	48.3542519350746
1973-01-01	47.8263921899110
1974-01-01	49.4213001451402
1975-01-01	50.1280498024200
1976-01-01	49.9520571897065
1977-01-01	48.8311101813262
1978-01-01	47.9401866539717
1979-01-01	47.4729832392302
1980-01-01	47.2940236985381
1981-01-01	47.0846285062806
1982-01-01	46.5428195650025
1983-01-01	45.3101111508425
1984-01-01	45.2535012773560
1985-01-01	45.1983852541294
1986-01-01	45.0216601946496
1987-01-01	44.8495961280933
1988-01-01	44.4127768366312
1989-01-01	43.5224345965529
1990-01-01	42.6397136646379
1991-01-01	41.7987227862529
1992-01-01	41.5583169379057
1993-01-01	41.7028768708598
1994-01-01	41.5982933628546
1995-01-01	41.5016449707375
1996-01-01	41.0533998270413
1997-01-01	40.3051830930908
1998-01-01	40.1841276379153
1999-01-01	40.3921556373547
2000-01-01	40.3413928784990
2001-01-01	39.9239437643897
2002-01-01	40.1738537043839
2003-01-01	39.9841264049002
2004-01-01	39.7381367112932
2005-01-01	39.1262168458263
2006-01-01	38.6025687973218
2007-01-01	37.9804311994132
2008-01-01	37.5780513139584
2009-01-01	36.9157203044033
2010-01-01	36.6997744139310
2011-01-01	36.3137670466598
2012-01-01	36.5557231613083
2013-01-01	34.9367386097528
2014-01-01	33.9095737226282
2015-01-01	33.0872218738946
2016-01-01	31.8118927078503
2017-01-01	30.5515018247563