Year	Number
1971	32.10988
1972	31.26784
1973	33.11104
1976	37.47284
1977	35.27954
1978	32.50973
1979	33.01417
1980	30.71847
1981	34.12378
1982	34.42476
1983	34.04722
1984	31.67137
1985	29.22474
1986	22.99501
1987	21.16076
1988	17.48231
1989	17.44251
1990	12.49244
1991	12.81626
1992	13.82129
1993	13.7903
1994	14.61121
1995	16.45318
1999	30.12094
2000	31.87973
2001	30.81717
2002	31.15684
2003	32.61077
2004	33.04292
2005	33.13514
2006	33.77265
2007	32.7813
2008	34.49797
2009	34.21812
2010	34.07819
2014	31.80264
2016	24.04989
2017	26.41848
2018	27.24679