Year	Number
1981	14.05
1986	12.74901
1989	12.35772
1990	13.00471
1991	11.70884
1992	10.8409
1993	9.91951
1994	9.47769
1999	8.89249
2001	13.21318
2002	11.87728
2003	11.55959
2004	10.64632
2005	10.73177
2006	10.58251
2007	10.64422
2008	10.41384
2009	10.02138
2011	9.70136
2012	9.65974
2013	9.47393
2014	9.34928