Year	Number
1971	36.68174
1972	36.0012
1973	34.64138
1974	31.50771
1975	31.14162
1976	30.86378
1977	30.93946
1978	32.43649
1979	32.79685
1980	34.55094
1981	36.59854
1982	39.30084
1983	47.07764
1984	52.30521
1985	54.25925
1986	56.20973
1987	62.35171
1988	70.73732
1989	68.90551
1990	65.87336
1991	66.89942
1992	65.85671
1993	62.60442
1996	45.01689
1998	47.85557
1999	55.41274
2000	55.35975
2001	50.19719
2002	49.07639
2003	49.90569
2004	51.24546
2005	48.70398
2006	54.18522
2007	51.99833
2009	51.36121
2010	50.6021
2011	48.31143
2012	47.10468
2013	45.00022
2014	43.65376
2015	43.22109
2016	49.66066
2017	49.61434
2018	42.52383