Year	Number
1971	41.46762
1972	38.98198
1973	41.28752
1974	41.60084
1975	40.44125
1976	40.18729
1977	41.47087
1978	37.32588
1979	37.48911
1980	36.98566
1981	36.48955
1982	36.09592
1983	34.97114
1984	36.1651
1985	38.14525
1986	39.27572
1987	40.33147
1988	40.56335
1989	40.66154
1990	41.07124
2000	32.99996
2001	34.7419
2002	35.00461
2003	34.82196
2004	37.4976
2005	38.33941
2006	39.00535
2007	39.95136
2008	40.66857
2009	39.68783
2010	40.45158
2011	39.83264
2012	41.35274
2013	42.54875
2014	46.52317
2015	46.34065
2016	47.63465
2017	44.78201
2018	44.0773