Year	Number
1971	33.07847
1972	30.27734
1973	29.15901
1974	28.30899
1975	29.77118
1976	31.48901
1978	33.62505
1981	34.14035
1982	34.35011
1983	34.25573
1984	34.98342
1985	32.1134
1986	32.3135
1987	33.84303
1988	34.05541
1989	33.44644
1990	33.34573
1991	33.09292
1992	32.44527
1994	34.02598
1995	36.20277
1997	31.59721
1998	33.62201
1999	34.06824
2001	36.38671
2002	38.3308
2003	37.08653
2004	37.53937
2005	37.86897
2006	37.27093
2007	35.13372
2009	34.81426
2014	26.99059
2015	26.22974
2016	23.52214
2017	23.88062