Year	Percent
1968-01-01	2.34823721469350
1969-01-01	2.49126190891761
1970-01-01	2.47883018769891
1971-01-01	2.30819424356714
1972-01-01	2.32333846497399
1973-01-01	2.16667961201174
1974-01-01	2.25627089772058
1975-01-01	2.47696577164824
1976-01-01	2.43399545665549
1977-01-01	2.58940768305284
1978-01-01	2.50413640808413
1979-01-01	2.33928460482315
1980-01-01	2.43991385290190
1981-01-01	2.48441498801930
1982-01-01	2.37311067954250
1983-01-01	2.27140518571057
1984-01-01	2.31383911296458
1985-01-01	2.53519606768971
1986-01-01	2.57002067069638
1987-01-01	2.52445251217780
1988-01-01	2.40081982192121
1989-01-01	2.31503950101259
1990-01-01	2.29764187937831
1991-01-01	2.18392131986425
1992-01-01	2.07231129992137
1993-01-01	2.13877273200297
1994-01-01	2.46413588333941
1995-01-01	2.45623828026199
1996-01-01	2.28680633623373
1997-01-01	2.29376475646301
1998-01-01	2.58306813220818
1999-01-01	2.63625461469115
2000-01-01	2.67539455544328
2001-01-01	2.99890166477151
2002-01-01	3.35435368194087
2003-01-01	3.42879524588335
2004-01-01	3.63610469136869
2005-01-01	3.81632253200126
2006-01-01	3.72451161855695
2007-01-01	3.62343639169011
2008-01-01	3.74467465683398
2009-01-01	3.87111390302113
2010-01-01	3.74737793995619
2011-01-01	3.94690078164997
2012-01-01	4.33376629895215
2013-01-01	4.28484251070568
2014-01-01	4.38546120667958
2015-01-01	4.44665158801470
2016-01-01	4.35353908392275
2017-01-01	4.40950701035907