Annual % of total
1960 96.02612608686673
1961 96.20098474203424
1962 96.38701005026452
1963 96.43044142352139
1964 96.56313379476443
1965 96.92506310108831
1966 96.67282032327556
1967 96.51037089654052
1968 96.13213329639139
1969 96.30037291677783
1970 96.72091820178781
1971 67.37176673971462
1972 68.04089220555336
1973 68.91978979835291
1974 69.06654592443003
1975 70.52788868942011
1976 71.2386823195965
1977 72.59808157993587
1978 74.3201673898012
1979 74.32428350082996
1980 74.01266432940685
1981 72.91328295755162
1982 73.25108085792493
1983 73.7370664539304
1984 74.09202379228674
1985 73.8400588003076
1986 74.55205165634986
1987 75.11264413359294
1988 75.69902925757393
1989 75.57895999803388
1990 83.1428545844349
1991 82.71497327884131
1992 82.36297709293906
1993 82.25332308793733
1994 81.7236510658656
1995 82.1389788849112
1996 82.28884487888176
1997 82.1537454464677
1998 82.02306104622296
1999 81.89191072761686
2000 82.23099479174579
2001 82.5342710914742
2002 82.57737774349255
2003 83.59668447265207
2004 84.22106320272081
2005 84.75466218948989
2006 85.32363796274275
2007 85.67882139635726
2008 85.58686813325859
2009 85.29799263748514
2010 85.66001193674295
2011 86.4875007442724
2012 86.04695793746276
2013 86.08624935039828
2014 86.18233309317407
2015 78.99368880656947