Year	Number
1971	38.82783
1972	38.31777
1973	38.28493
1974	37.44914
1975	35.67201
1976	34.66343
1977	34.50828
1978	32.49118
1979	32.23471
1980	32.18107
1981	31.76893
1982	31.40796
1983	31.80441
1984	32.14243
1985	31.91506
1986	31.26839
1987	29.40801
1988	29.83301
1989	28.39694
1991	26.48989
1995	24.27996
1998	23.6915
2002	20.05269
2003	19.93241
2014	16.90871
2016	18.36314
2017	21.03903
2018	18.53699