Every 17 years, swarms of cicadas emerge from the ground in the eastern United States, live for about six weeks, and then die. (There are several different “broods,” so we experience cicada eruptions more often than every 17 years.) There are so many cicadas that their dead bodies can serve as fertilizer and increase plant growth. In a study, a researcher added 10 dead cicadas under 39 randomly selected plants in a natural plot of American bellflowers on the forest floor, leaving other plants undisturbed. One of the response variables measured was the size of seeds produced by the plants. Here are the boxplots and summary statistics of seed mass (in milligrams) for 39 cicada plants and 33 undisturbed (control) plants:

Variable: n Minimum Q1 Median Q3 Maximum Cicada plants: 39 0.17 0.22 0.25 0.28 0.35 Control plants: 33 0.14 0.19 0.25 0.26 0.29

(a) Write a few sentences comparing the distributions of seed mass for the two groups of plants.

(b) Based on the graphical displays, which distribution has the larger mean? Justify your answer.

(c) Explain the purpose of the random assignment in this study.

(d) Name one benefit and one drawback of only using American bellflowers in the study

Transcribed Image Text:

Cicada Plants Control Plants- 0.15 0.30 0.35 0.25 0.20 Seed Mass (milligrams)