Year Number 1984 4.783303579420262 1985 4.995641744372839 1986 5.2830168435466485 1987 4.577302331890253 1988 4.848358663703066 1989 5.403290905184055 1990 3.534741613570762 1991 3.4438788247627348 1992 3.9108044646975 1993 4.38282317432384 1994 4.6258607696525 1995 4.978261241465715 1996 4.321119983311881 1997 4.769126511902155 1998 4.580950966089304 1999 4.14570964614308 2000 4.365701776066821 2001 4.5272106911277925 2002 4.995803193498055 2003 4.330488680833128 2004 5.256571196040931 2005 6.159751683266843 2006 5.100145682080505 2007 5.026342043951585 2008 4.5814244889404705 2009 3.890219188889017 2010 4.239215735302148 2011 4.130910301507427 2012 4.666015557443498 2013 2.9192756830981788 2014 3.3602186927726785 2015 4.309623505582213 2016 4.19777099115772 2017 3.7495110795912514 2018 4.3344899402467085 2019 4.267270766890156 2020 3.7249542374636646 2021 4.5749285489828635 2022 4.489873930230852 2023 5.676196969832455