Year	Number
1971	65.03154
1972	64.58207
1973	62.14742
1974	63.23729
1975	60.62784
1976	60.13912
1977	54.77625
1978	51.11015
1979	46.02873
1980	46.35147
1981	43.66872
1982	41.03095
1983	38.76261
1984	38.25595
1985	38.2746
1988	39.73739
1989	40.48509
1990	39.86929
1991	40.34421
1992	37.76383
1993	38.46674
1994	39.93704
1995	38.05827
1996	37.10923
1998	46.55921
1999	47.15347
2000	47.95381
2001	46.69824
2002	47.48805
2003	51.64584
2004	52.38012
2005	53.5879
2006	48.14341
2007	48.7325
2008	47.15533
2009	47.90319
2010	40.14191
2011	43.24486
2012	43.06725
2013	39.76644
2014	41.71542
2015	41.1927
2016	40.606
2018	39.81169