Annual % of total
1960 99.02015892157824
1961 99.04098583712091
1962 99.19266888828312
1963 99.30220699039042
1964 99.39761102012736
1965 99.10230936200503
1966 98.86613590207108
1967 98.77118596782275
1968 98.7821979763326
1969 98.63853600621097
1970 97.8669903112039
1971 98.0588816459674
1972 97.65361238772628
1973 97.62143893372101
1974 97.18269289767291
1975 96.22976002271247
1976 96.33004313491435
1977 95.20012737388139
1978 95.1884250975718
1979 94.83350375494135
1980 94.09208558741216
1981 92.97445558300925
1982 91.96987315651253
1983 91.65331347875984
1984 90.06462342232105
1985 87.92519035349943
1986 88.65357082848864
1987 87.90540583825604
1988 86.91009482983641
1989 86.4511843360393
1990 86.83788464222155
1991 87.09636476880391
1992 85.95284872182337
1993 86.00930916416696
1994 86.02180942313717
1995 85.81095470567577
1996 85.90869753410128
1997 84.62946066242358
1998 84.92246199140767
1999 83.93137164289224
2000 83.62197513548057
2001 83.60503301880446
2002 83.27815679295443
2003 83.18231408790263
2004 82.56602161666581
2005 81.85567626825777
2006 81.2718831767448
2007 81.27195015647062
2008 80.80225178337086
2009 79.96746885381566
2010 79.56035025958603
2011 80.3702087567313
2012 80.62522297866155
2013 81.08826801353561
2014 79.71052693699183
2015 78.86255105675498