Year	Number
1972	3.1260689729341653
1973	2.733501512566499
1974	2.504607176767297
1975	2.063438619409051
1976	2.1103413279512697
1977	1.952406724711793
1978	2.255656701128094
1979	1.3939723071855057
1980	1.335699386868495
1981	1.5293729832293543
1982	1.6531945013242688
1983	2.338044595194282
1984	2.265396670712992
1985	2.2899476337281133
1986	2.1155829001424413
1987	1.550857212179359
1988	2.1603847422264355
1989	1.8854805121880387
1990	1.709009177087689
1991	1.2172709550201435
1992	1.3687589110806428
1993	1.7849409739760917
1994	2.0784391668886055
1995	2.0235978435564963
1996	2.0538832206788475
1997	2.456147363836026
1998	2.7421018608659593
1999	2.067854723795057
2000	2.5420318821230574
2001	2.833163584334081
2002	2.3041891066816986
2003	2.084150804328105
2004	2.1668747578126126
2005	2.1759510726935085
2006	2.3536742352429587
2007	1.6688651879519847
2008	1.6915533046258011
2009	1.6814665120684886
2010	1.75408171164185
2011	1.7840768779873282
2012	1.9706637480797131
2013	1.9301491271433568
2014	2.112870563281886
2015	2.2453702515345944
2016	1.979739623102716
2017	2.5975465852312696