A researcher wishes to see if a kelp extract helps prevent frost damage on tomato plants. One hundred tomato plants in individual containers are randomly assigned to two different groups. Plants in both groups are treated identically, except that the plants in group 1 are sprayed weekly with a kelp extract, while the plants in group 2 are not. After the first frost in the autumn, 8 of the 50 plants in group 1 exhibited damage, and 18 of the 50 plants in group 2 showed damage. Why would the use of z-procedures be questionable value in this situation