Year	Number
1971	37.98025
1976	35.35867
1977	33.36982
1978	34.52648
1979	34.44526
1980	33.10761
1982	34.4931
1983	31.34519
1984	32.23946
1986	31.87956
1987	31.32996
1988	29.86008
1989	19.6581
1990	25.14449
1991	24.93352
1992	23.95754
1993	23.50758
1994	26.76104
1995	25.09622
1996	27.02079
1997	23.12247
1999	23.37189
2000	22.98104
2001	22.26153
2002	22.49667
2003	22.18727
2004	21.8606
2005	25.6326
2006	26.00118
2007	27.08402
2009	27.20919
2010	27.73437
2016	23.07766
2017	23.77693
2018	23.67945