Year	Percent
1979-01-01	13.3714347884302
1980-01-01	13.2952580695664
1981-01-01	13.4681601846874
1982-01-01	13.9702573581165
1983-01-01	14.6916349357500
1984-01-01	15.1355694379648
1985-01-01	15.5573863491125
1986-01-01	15.2076514410774
1987-01-01	15.6445362694406
1988-01-01	15.6602284339240
1989-01-01	15.3059810143156
1990-01-01	14.9951235741891
1991-01-01	15.8218052672361
1992-01-01	16.2481834997559
1993-01-01	16.5860314328248
1994-01-01	16.4938697615089
1995-01-01	16.1821042089644
1996-01-01	16.3044494131399
1997-01-01	16.9135375800861
1998-01-01	17.1420957743858
1999-01-01	17.5032306398966
2000-01-01	17.6735956339296
2001-01-01	17.8161026554213
2002-01-01	17.8488782843386
2003-01-01	18.0306857816250
2004-01-01	17.9866587385119
2005-01-01	17.3826819956304
2006-01-01	17.2559712789500
2007-01-01	17.0354868274154
2008-01-01	16.9545600284042
2009-01-01	17.3872670256486
2010-01-01	17.1027437165317
2011-01-01	17.1569673238807
2012-01-01	17.5200444313786
2013-01-01	17.6190197365403
2014-01-01	17.8825737267082
2015-01-01	17.3115047818689
2016-01-01	17.6696924601610
2017-01-01	17.3950622312087