Year	Percent of Total
1960-01-01	37.7327782765252
1961-01-01	38.3888862934124
1962-01-01	37.8459905361585
1963-01-01	36.7939395305677
1964-01-01	36.2666751557653
1965-01-01	36.7363205094232
1966-01-01	36.6416156637638
1967-01-01	37.9071087934123
1968-01-01	39.7499497060319
1969-01-01	41.1119316955857
1970-01-01	41.5942791317382
1971-01-01	42.2665121984702
1972-01-01	41.9646376842471
1973-01-01	41.0991069206356
1974-01-01	40.2703585075248
1975-01-01	39.7292982867929
1976-01-01	39.0363826784174
1977-01-01	38.4941623228255
1978-01-01	38.0108219431108
1979-01-01	37.4129726115602
1980-01-01	36.6431244255140
1981-01-01	35.4478454117396
1982-01-01	34.4469275840095
1983-01-01	33.5080188700384
1984-01-01	32.4791510423430
1985-01-01	31.3171238292382
1986-01-01	30.6511136126894
1987-01-01	29.6241104743488
1988-01-01	28.4888166283859
1989-01-01	27.6049146345947
1990-01-01	27.1262768038758
1991-01-01	26.6579892911644
1992-01-01	26.6209650441860
1993-01-01	26.8355898950401
1994-01-01	26.9958145298295
1995-01-01	26.9500110669971
1996-01-01	26.9867594291065
1997-01-01	26.8171386015479
1998-01-01	26.5050048506177
1999-01-01	26.1886456462117
2000-01-01	25.9383075854565
2001-01-01	25.6655661619216
2002-01-01	25.4552436141198
2003-01-01	25.2701441975586
2004-01-01	25.0376472355210
2005-01-01	24.7226519125306
2006-01-01	24.4244308561659
2007-01-01	24.0383734623836
2008-01-01	23.5981325117178
2009-01-01	23.1649844064639
2010-01-01	22.7728745902208
2011-01-01	22.3618694346294
2012-01-01	22.0153798775684
2013-01-01	21.7120515924613
2014-01-01	21.4141593669434
2015-01-01	21.1069462793749
2016-01-01	20.8696807315494
2017-01-01	20.6171245380471