Question

Exercise 15-9 (LO15-2)

The Damon family owns a large grape vineyard in western New York along Lake Erie. The grapevines must be sprayed at the beginning of the growing season to protect against various insects and diseases. Two new insecticides have just been marketed: Pernod 5 and Action. To test their effectiveness, three long rows were selected and sprayed with Pernod 5, and three others were sprayed with Action. When the grapes ripened, 390 of the vines treated with Pernod 5 were checked for infestation. Likewise, a sample of 420 vines sprayed with Action were checked. The results are:

Insecticide	Number of Vines Checked (sample size)	Number of Infested Vines
Pernod 5	390	23
Action	420	46

At the 0.02 significance level, can we conclude that there is a difference in the proportion of vines infested using Pernod 5 as opposed to Action? Hint: For the calculations, assume the Pernod 5 as the first sample.

1. Compute the pooled proportion. (Do not round the intermediate values. Round your answer to 2 decimal places.)

pooled proportion

3. Compute the value of the test statistic. (Negative amount should be indicated by a minus sign. Do not round the intermediate values. Round your answer to 2 decimal places.)

Value of the test statistic

Answer 1

The statistical software output for this problem is:

Hence,

a) Pooled proportion = (23 + 46) / (390 + 420) = 0.09

b) Test statistic = - 2.58