Year	Number
1971	14.38854
1972	14.97959
1973	16.80407
1974	16.77459
1975	14.60283
1976	14.89711
1977	14.73968
1978	15.30578
1982	19.74487
1983	20.04706
1984	23.77876
1985	17.74029
1986	23.29996
1988	22.89638
1989	24.8228
1990	20.20058
1992	22.44231
1993	22.04933
1994	20.0785
1996	20.53931
1997	21.41403
2000	29.90326
2002	24.59008
2003	26.79364
2004	26.8001
2005	26.39959
2006	26.40074
2007	25.47361
2008	26.31464
2010	24.63368
2015	22.45316
2016	15.83443
2017	12.50293