Year	Number
1970	1302
1971	1530
1972	1703
1973	1895
1974	2221
1975	2473
1976	2304
1977	2421
1978	2543
1979	3059
1980	2844
1981	2765
1982	3028
1983	2874
1984	3708
1985	3588
1986	4241
1987	4440
1991	5992
1992	6653
1998	1993
1999	1722
2000	2733
2001	2895
2002	2649
2003	2319
2004	2840
2006	2226
2007	2863
2008	3351
2009	2387
2011	2024
2012	1389