| Year |
| Acid Spike | No Acid Spike | Total | χ2 | P |
| 1990 |
|
|
|
|
|
|
|
| Day-class Gap | 7 | 5 | 12 | 4.69 | 0.018 |
|
| No Day-Class Gap | 3 | 17 | 20 |
|
|
| 1991 |
|
|
|
|
|
|
|
| Day-class Gap | 0 | 4 | 4 | 0.01 | >0.50 |
|
| No Day-class Gap | 0 | 12 | 12 |
|
|
| 1992 |
|
|
|
|
|
|
|
| Day-class Gap | 3 | 2 | 5 | 4.40 | 0.021 |
|
| No Day-class Gap | 1 | 16 | 17 |
|
|
| 1990-1992 TOTAL |
|
|
|
|
|
|
|
| Day-class Gap | 10 | 11 | 21 | 11.94 | 0.000 |
|
| No Day-class Gap | 4 | 45 | 49 |
|
|