Year	Number
1973	26.76199
1974	27.06082
1975	26.05464
1976	26.33765
1977	26.94185
1978	26.40439
1979	27.09744
1980	27.82283
1981	26.9037
1982	25.82808
1983	25.57189
1984	25.28131
1985	25.14173
1986	25.39895
1987	24.95823
1988	25.425
1989	25.21432
1990	24.12447
1991	24.47725
1992	25.7258
1993	26.5388
1994	26.90126
1995	26.94286
1996	27.40007
1997	26.70555
1998	26.64463
1999	25.80915
2000	25.10662
2001	24.52632
2002	23.30413
2003	22.30679
2004	21.11884
2005	20.35432
2006	21.99684
2007	21.1369
2008	20.53064
2009	20.76313
2010	21.62473
2011	21.3648
2012	21.59666
2013	21.05264
2014	19.67689
2015	18.95301
2016	18.48128
2017	17.73676
2018	17.2514