Year	Percent
1968-01-01	54.1172095104649
1969-01-01	53.6088659939114
1970-01-01	53.4569859423780
1971-01-01	52.5346176466817
1972-01-01	51.6457480649254
1973-01-01	52.1736078100890
1974-01-01	50.5786998548598
1975-01-01	49.8719501975800
1976-01-01	50.0479428102935
1977-01-01	51.1688898186738
1978-01-01	52.0598133460283
1979-01-01	52.5270167607698
1980-01-01	52.7059763014619
1981-01-01	52.9153714937194
1982-01-01	53.4571804349975
1983-01-01	54.6898888491575
1984-01-01	54.7464987226440
1985-01-01	54.8016147458706
1986-01-01	54.9783398053504
1987-01-01	55.1504038719067
1988-01-01	55.5872231633688
1989-01-01	56.4775654034471
1990-01-01	57.3602863353621
1991-01-01	58.2012772137470
1992-01-01	58.4416830620943
1993-01-01	58.2971231291402
1994-01-01	58.4017066371454
1995-01-01	58.4983550292625
1996-01-01	58.9466001729587
1997-01-01	59.6948169069092
1998-01-01	59.8158723620847
1999-01-01	59.6078443626453
2000-01-01	59.6586071215010
2001-01-01	60.0760562356103
2002-01-01	59.8261462956161
2003-01-01	60.0158735950998
2004-01-01	60.2618632887068
2005-01-01	60.8737831541737
2006-01-01	61.3974312026782
2007-01-01	62.0195688005868
2008-01-01	62.4219486860416
2009-01-01	63.0842796955967
2010-01-01	63.3002255860690
2011-01-01	63.6862329533402
2012-01-01	63.4442768386917
2013-01-01	65.0632613902472
2014-01-01	66.0904262773718
2015-01-01	66.9127781261054
2016-01-01	68.1881072921497
2017-01-01	69.4484981752437