Annual % of total
1960 4.201117318435753
1961 3.9049919484702094
1962 5.526216522067144
1963 6.141107469380715
1964 6.368243243243244
1965 7.450729049831757
1966 8.61288812607271
1967 8.531157270029674
1968 8.187456926257752
1969 8.65472610798797
1970 9.566227730441518
1971 9.939540507859732
1972 11.24053581828771
1973 10.946681175190424
1974 9.790912746280659
1975 10.031668198998878
1976 9.723693077885818
1977 10.687663063734625
1978 13.372041875604824
1979 13.452174630684164
1980 15.58366402116402
1981 16.61992741669416
1982 16.83571599712483
1983 17.144975899147198
1984 17.406603279179457
1985 15.205032972030624
1986 14.055265123226288
1987 14.243172574084834
1988 14.3756118025451
1989 13.28098091892264
1990 17.149191567744577
1991 17.204015421115063
1992 15.733435444465327
1993 15.508162423807814
1994 15.920875420875419
1995 14.057040298002033
1996 17.40345114698386
1997 19.600775279131938
1998 20.33471368388204
1999 20.06446930374083
2000 21.46536585365854
2001 22.662009904371583
2002 23.49141414141414
2003 22.655278471974295
2004 23.76179473496976
2005 24.20815230530133
2006 24.33231115731116
2007 23.7280114884271
2008 29.219878333333334
2009 31.94646601016518
2010 34.02236703772418
2011 30.134337004720358
2012 32.60598947218665
2013 29.726317007327417
2014 28.41902029566525
2015 28.53317906948044
2016 26.158458691499526