| Value | Category | Cases | |
|---|---|---|---|
| 99 | Don’t Know | 0 | 
                                    
                                    0%
                                 | 
| 1962 | 2 | 
                                    
                                    0.5%
                                 | |
| 1964 | 4 | 
                                    
                                    1.1%
                                 | |
| 1966 | 1 | 
                                    
                                    0.3%
                                 | |
| 1968 | 6 | 
                                    
                                    1.6%
                                 | |
| 1969 | 3 | 
                                    
                                    0.8%
                                 | |
| 1970 | 5 | 
                                    
                                    1.4%
                                 | |
| 1971 | 5 | 
                                    
                                    1.4%
                                 | |
| 1972 | 6 | 
                                    
                                    1.6%
                                 | |
| 1973 | 8 | 
                                    
                                    2.2%
                                 | |
| 1974 | 7 | 
                                    
                                    1.9%
                                 | |
| 1975 | 10 | 
                                    
                                    2.7%
                                 | |
| 1976 | 13 | 
                                    
                                    3.5%
                                 | |
| 1977 | 8 | 
                                    
                                    2.2%
                                 | |
| 1978 | 18 | 
                                    
                                    4.9%
                                 | |
| 1979 | 9 | 
                                    
                                    2.5%
                                 | |
| 1980 | 21 | 
                                    
                                    5.7%
                                 | |
| 1981 | 13 | 
                                    
                                    3.5%
                                 | |
| 1982 | 29 | 
                                    
                                    7.9%
                                 | |
| 1983 | 30 | 
                                    
                                    8.2%
                                 | |
| 1984 | 34 | 
                                    
                                    9.3%
                                 | |
| 1985 | 28 | 
                                    
                                    7.6%
                                 | |
| 1986 | 35 | 
                                    
                                    9.5%
                                 | |
| 1987 | 56 | 
                                    
                                    15.3%
                                 | |
| 1988 | 16 | 
                                    
                                    4.4%
                                 |