Annual % of total
1960 74.49344866009767
1961 72.75348152733243
1962 73.22551467928564
1963 74.98480542512813
1964 74.74404504936321
1965 75.18439325894046
1966 77.2890476804452
1967 75.9352781868375
1968 77.81746146322392
1969 80.2502525781461
1970 81.83017167540537
1971 79.11746625008558
1972 78.22607077002371
1973 76.03950586617789
1974 74.86175795839979
1975 69.962635070176
1976 70.29042006832618
1977 68.79456932354832
1978 64.37363313486782
1979 65.8912631127779
1980 60.12571363418595
1981 55.14980362708266
1982 52.31005014237373
1983 48.32813101067023
1984 44.1086153917406
1985 43.4266348352962
1986 41.75551157724945
1987 40.00648716072786
1988 40.042882345035544
1989 39.09301733495724
1990 37.294957170813426
1991 35.52821961440979
1992 36.90834969881652
1993 36.877335384727594
1994 36.9024796082203
1995 36.8532278929887
1996 36.7164871066478
1997 35.637368824944794
1998 35.04731519533755
1999 34.84981229253483
2000 34.82918337265837
2001 33.98788812090221
2002 37.44624962167069
2003 36.521810320211124
2004 34.83201035455226
2005 33.81150917406153
2006 33.41258418676985
2007 32.452471951532644
2008 33.112640059417835
2009 31.983995335647116
2010 34.4232514038991
2011 34.21418704525978
2012 30.999155778788683
2013 30.01601560924334
2014 29.774747265134426
2015 25.11709613465313