Year	Number
1979	9.9821
1980	10.40426
1982	11.04393
1983	9.79284
1984	10.46293
1985	11.35383
1986	10.58713
1987	10.69591
1988	10.82249
1989	10.22202
1990	11.93942
1991	12.26319
1992	11.81501
1993	14.80809
1994	15.61934
1995	14.08583
2000	18.35885
2001	18.35886
2002	18.08923
2003	16.06749
2004	15.53104
2005	15.39937
2006	15.92954
2007	19.00923
2008	15.05623
2009	14.83169
2010	14.22568
2011	15.09928
2012	19.52833
2013	16.17493
2014	13.91286
2015	15.94918
2017	13.90184
2018	13.34506