Annual % of total
1960 37.451975850713495
1961 38.64562787639711
1962 39.804822043628015
1963 40.28268551236749
1964 41.85396115122547
1965 42.57499534190423
1966 42.81482772139217
1967 43.01066709122751
1968 41.871019691091426
1969 41.248727296613794
1970 41.03190352617921
1971 41.82549396747683
1972 41.22175454142668
1973 39.73337380789761
1974 42.465320797803855
1975 43.14545290182607
1976 43.70842862838079
1977 41.57245632065776
1978 39.526835356859195
1979 37.76323171872078
1980 39.10627028236786
1981 40.77946592149823
1982 41.449389375889716
1983 40.25852927194939
1984 36.34602344279764
1985 35.29189780746444
1986 34.809345862206584
1987 32.14594351688616
1988 31.653597587246878
1989 31.11461205198897
1990 38.26102299716156
1991 38.279688860795055
1992 38.529840463528856
1993 39.66868582114927
1994 36.93445477452429
1995 36.49990805930589
1996 35.88009358612344
1997 32.18566831246694
1998 34.530086527819705
1999 36.78151111111111
2000 35.25072907290729
2001 32.076021676761236
2002 33.35132385938669
2003 33.86508733186107
2004 33.00034632482166
2005 33.28278050307901
2006 32.867349909035774
2007 30.30864475321443
2008 29.252037601092322
2009 30.093810233482365
2010 31.88160774193548
2011 30.29697677188803
2012 30.20014315428851
2013 31.292480211081795
2014 29.984054054054056
2015 28.018093278463645
2016 28.99991847062131