Year	Percent of Total
1960-01-01	31.1776819769864
1961-01-01	31.5016651228660
1962-01-01	31.7718896992189
1963-01-01	32.0153409586162
1964-01-01	32.2624186456760
1965-01-01	32.5324735075895
1966-01-01	32.9392119169046
1967-01-01	33.3198512882275
1968-01-01	33.6847667232754
1969-01-01	34.0355089360465
1970-01-01	34.3688889340776
1971-01-01	35.0374170518056
1972-01-01	35.6187910093081
1973-01-01	36.1401553902286
1974-01-01	36.6316106901881
1975-01-01	37.1043655997390
1976-01-01	37.6283953779171
1977-01-01	38.1148953849146
1978-01-01	38.5577460085328
1979-01-01	38.9452070388865
1980-01-01	39.2746986596888
1981-01-01	39.6681590236320
1982-01-01	39.9893069745910
1983-01-01	40.2528293687652
1984-01-01	40.4798764483351
1985-01-01	40.6817374124337
1986-01-01	40.9559134704998
1987-01-01	41.1745050253004
1988-01-01	41.3485708707450
1989-01-01	41.4826110323303
1990-01-01	41.5762456259740
1991-01-01	41.7081790143965
1992-01-01	41.7851128124888
1993-01-01	41.8091447052072
1994-01-01	41.7804343780788
1995-01-01	41.6990674288787
1996-01-01	41.5978003472191
1997-01-01	41.4515496479107
1998-01-01	41.2628156526847
1999-01-01	41.0329013060753
2000-01-01	40.7654156127500
2001-01-01	40.4565148673925
2002-01-01	40.1010808793820
2003-01-01	39.7225154463440
2004-01-01	39.3501709787019
2005-01-01	39.0026982608832
2006-01-01	38.5182068098701
2007-01-01	38.0761257943060
2008-01-01	37.6787200820614
2009-01-01	37.3193954450406
2010-01-01	36.9964821577725
2011-01-01	36.7351147633523
2012-01-01	36.4775614079327
2013-01-01	36.2338913678807
2014-01-01	35.9993773034574
2015-01-01	35.7614205965780
2016-01-01	35.8623103709189
2017-01-01	35.9021142767131