Year	Number
1971	58.45613
1972	60.37813
1973	59.48617
1974	59.50325
1975	58.54683
1976	59.68668
1977	60.56694
1978	58.12109
1979	55.43369
1980	54.29058
1981	55.07967
1982	51.83896
1983	48.20139
1984	45.08388
1985	44.42142
1986	46.06011
1987	50.25659
1988	51.66419
1989	54.61232
1990	55.63861
1991	58.25862
1992	63.78768
1994	53.10531
1995	54.86158
1996	50.84948
1997	46.37572
1998	45.51107
1999	41.28126
2000	37.45983
2001	34.33866
2002	35.20108
2003	35.45168
2004	39.08429
2005	33.59536
2006	37.56283
2007	39.13792
2008	41.32555
2009	43.50925
2010	40.57306
2011	40.94767
2012	41.67781
2013	41.08672
2014	41.13664
2015	44.20973
2016	41.39676
2017	40.12613
2018	40.14504