Purple Loosestrife (lythrum salicaria) is a hearty plant with an aggressive rate of growth. When introduced into
a wetland ecosystem, the plant will grow quickly and "choke" out other vegetation until it becomes the
dominant species. This rapid change in biodiversity has experts concerned about the state or health of the
Northern Ontario wetlands and several studies have been conducted to determine how to control the growth
and spread of Purple Loosestrife.
One such study involved the release of Galerucella beetles; an insect which feeds almost exclusively on the
plant. Before the beetles were released, the growth rate of lythrum salicaria was assessed in five test zones. A
month after the release of the beetles, the growth rates at the test zones were re-observed. The growth rates
before and were as follows:
Baseline Data: 3.0, 2.0, 2.5, 1.0, 2.5
After Data: 4.5, -1.5, -0.5, -0.5, -1.0
a. Would a one tailed or two tailed hypothesis be more appropriate?
b. What t-test would be the best match for this experimental design?
c. calculate the z-test statistic
d. calculate the cohens d
e. calculate the confidence interval for the predicted mean
f. what is a reasonable conclusion for this study? Report this in the appropriate APA formatted statistic
g. Then, assuming your hypothesis is correct, describe what could you to the data to re-evaluate the t-statistic? Recalculate the t-test after making your proposed changes and reinterpret the results