The surface of plant leaves is a thriving ecosystem, home to many microorganisms such as bacteria. These bacteria can affect the health of the plant, because some cause disease and some serve as ice-nucleation sites, thus causing frost damage. Hirano et al. (1982) were interested in the probability distribution of the number of bacteria on corn plant leaves. The frequency distribution of the number of bacteria on a random sample of single leaves is shown in the accompanying figure. The number of bacteria is calculated as the number per gram of leaf.

a. Imagine that we wished to estimate the mean number of bacteria per gram of leaf and the uncertainty of our estimate. Would a confidence interval for the mean based on the t-distribution be appropriate? Explain your answer.

b. Name two appropriate methods to calculate a confidence interval for the mean with these data.

c. The authors also measured the frequency distribution of the number of bacteria on soybean leaves. The distribution was shaped similarly to the one shown here for corn leaves. List two valid methods that could be used to test for a difference in the median numbers of bacteria on corn and soybean leaves.

Transcribed Image Text:

Frequency 14 12- 10 8- 6 4 2- 0 0 50 100 150 200 250 Bacteria per gram of leaf (X 104)