Year	Number
1981	7.47791
1986	5.85484
1991	7.22975
1993	6.36139
1997	7.62244
1999	12.77697
2000	10.72448
2001	10.44955
2002	10.30732
2003	10.03163
2004	9.70725
2005	9.65026
2006	9.8946
2007	10.73454