Year	Number
1970	39.4106
1971	38.82618
1972	39.5245
1973	40.50665
1974	41.17758
1975	41.45978
1976	41.47875
1977	41.04906
1978	40.02739
1979	39.76398
1980	41.36342
1981	42.09154
1982	41.66373
1983	40.71023
1984	39.28688
1985	38.57209
1986	37.72056
1987	37.94714
1988	39.19857
1989	39.47372
1990	39.38734
1991	39.71738
1992	39.43715
1993	39.51132
1994	40.2696
1995	40.37475
1996	40.05168
1997	41.089
1998	40.95596
1999	40.23509
2000	41.56662
2001	41.81829
2002	42.92273
2003	43.45035
2004	43.01005
2005	43.01487
2006	42.5563
2007	42.14318
2008	41.9291
2009	41.58895
2010	40.50759
2011	39.87939
2012	38.97507
2013	38.49187
2014	37.82136
2015	36.95185
2016	36.21857
2017	35.93808
2018	35.97722