| Value | Category | Cases | |
|---|---|---|---|
| 1968 | 1 |
0.2%
|
|
| 1970 | 1 |
0.2%
|
|
| 1972 | 7 |
1.7%
|
|
| 1973 | 2 |
0.5%
|
|
| 1974 | 5 |
1.2%
|
|
| 1975 | 3 |
0.7%
|
|
| 1976 | 8 |
1.9%
|
|
| 1977 | 12 |
2.9%
|
|
| 1978 | 10 |
2.4%
|
|
| 1979 | 7 |
1.7%
|
|
| 1980 | 19 |
4.6%
|
|
| 1981 | 12 |
2.9%
|
|
| 1982 | 13 |
3.1%
|
|
| 1983 | 17 |
4.1%
|
|
| 1984 | 11 |
2.6%
|
|
| 1985 | 19 |
4.6%
|
|
| 1986 | 24 |
5.8%
|
|
| 1987 | 20 |
4.8%
|
|
| 1988 | 15 |
3.6%
|
|
| 1989 | 20 |
4.8%
|
|
| 1990 | 15 |
3.6%
|
|
| 1991 | 22 |
5.3%
|
|
| 1992 | 24 |
5.8%
|
|
| 1993 | 23 |
5.5%
|
|
| 1994 | 32 |
7.7%
|
|
| 1995 | 25 |
6%
|
|
| 1996 | 26 |
6.2%
|
|
| 1997 | 10 |
2.4%
|
|
| 1998 | 10 |
2.4%
|
|
| 1999 | 3 |
0.7%
|
|
| 2000 | 1 |
0.2%
|