Year	Number
1981	10.55505
1982	9.97982
1983	10.14601
1984	10.77586
1985	10.25973
1986	11.09483
1987	11.53145
1988	11.47444
1990	13.10915
1991	13.12158
1992	14.71368
1993	14.10852
1994	13.25788
1995	13.39393
1996	13.43466
1997	13.68902
1999	32.23055
2000	33.64753
2001	32.46771
2002	31.79936
2003	32.63364
2004	25.19817
2005	25.07888
2006	21.8822
2007	20.67106
2008	19.43846
2009	18.27624
2010	16.53563
2011	14.85085
2012	14.15392
2013	13.59104
2014	12.6886
2015	12.03148
2016	11.30358