Year	Percent
1968-01-01	55.6306909799218
1969-01-01	55.1113485150502
1970-01-01	54.7188776893268
1971-01-01	53.3549028142087
1972-01-01	53.0830060541446
1973-01-01	53.9339627769898
1974-01-01	52.5358768674211
1975-01-01	51.7079349421616
1976-01-01	52.2040012771478
1977-01-01	53.5059214971426
1978-01-01	54.5975669791203
1979-01-01	55.3490319218641
1980-01-01	55.7891637997807
1981-01-01	56.2432711953513
1982-01-01	57.0845023197323
1983-01-01	58.2905329995993
1984-01-01	58.7553822326414
1985-01-01	59.2389343025194
1986-01-01	59.6181077347477
1987-01-01	60.1407745288865
1988-01-01	61.0614573511802
1989-01-01	62.2850648232420
1990-01-01	63.2402926797722
1991-01-01	64.0124816821979
1992-01-01	64.2092532109466
1993-01-01	63.6523917810658
1994-01-01	63.5048214241240
1995-01-01	63.3089433795730
1996-01-01	63.7907164067306
1997-01-01	64.5792371979896
1998-01-01	64.1169162346605
1999-01-01	63.6146100799942
2000-01-01	63.6696888202935
2001-01-01	64.2090108345524
2002-01-01	63.9371198284785
2003-01-01	64.4759623453448
2004-01-01	65.1436703043563
2005-01-01	65.8084662631790
2006-01-01	66.6901016770525
2007-01-01	67.4753593279855
2008-01-01	67.6541653949866
2009-01-01	67.7582871945445
2010-01-01	68.2834605195490
2011-01-01	69.0671834286094
2012-01-01	69.1849343031735
2013-01-01	70.8740230723868
2014-01-01	71.9850379277650
2015-01-01	72.8308471998626
2016-01-01	74.0206566480774
2017-01-01	75.3437067969104