Year	Number
1971	45.23103
1972	44.08834
1973	45.99383
1974	40.76164
1975	41.51319
1976	41.16576
1977	43.3411
1978	42.33875
1979	42.92144
1980	42.76978
1981	45.7491
1982	42.76204
1983	43.5987
1984	41.23968
1985	46.10986
1986	46.49176
1987	50.79365
1988	53.57222
1989	51.24208
1990	57.58706
1991	52.89294
1992	58.94987
1993	58.18609
1994	57.74123
1995	59.73722
1996	58.20279
1997	57.63011
1998	55.87384
1999	48.60013
2000	50.91758
2001	50.83597
2002	48.89238
2003	46.04819
2004	43.20416
2005	41.67137
2006	38.531
2007	34.20976
2008	36.43514
2009	34.65629
2010	33.65179
2011	33.31196
2012	32.69103
2013	32.24855
2014	32.23045
2015	32.09004
2016	31.74299
2017	32.81273
2018	36.31817