Annual % of total
1960 16.661312086358674
1961 19.49014900077678
1962 19.776347001016607
1963 20.584589286879364
1964 22.48639543923296
1965 22.18133558544972
1966 25.141460905349795
1967 23.86338310675284
1968 24.699703894072293
1969 24.18686224489796
1970 25.215167461761666
1971 31.305316218275603
1972 31.637855259302665
1973 35.54452715743038
1974 32.37346869051686
1975 37.056829282307646
1976 38.92441488681417
1977 39.42462600690449
1978 37.817638266068755
1979 39.260571811694845
1980 36.26524513367257
1981 34.41387559808612
1982 35.30543341708543
1983 36.79940131553035
1984 40.40360332008969
1985 36.1454071472537
1986 37.47698282500251
1987 36.94696844539897
1988 36.86355022109918
1989 35.9002863399023
1990 41.09728374709077
1991 42.106571930852624
1992 18.476778997613362
1993 36.19722534955511
1994 45.39129792440859
1995 48.92469129468103
1996 49.12539232948021
1997 48.34839549768263
1998 60.62780712345306
1999 61.07735409475996
2000 39.742432472654215
2001 44.373130599461
2002 38.29972180244539
2003 37.55687762490949
2004 35.82993484657419
2005 33.05117344672209
2006 37.90056975115084
2007 37.999701531614086
2008 34.2139690500948
2009 33.13564997254926
2010 34.55837281213536
2011 28.156474908919964
2012 27.066379600935143
2013 25.869075021312877
2014 24.786077515264136
2015 26.726415343915345
2016 30.110310378872025