A historic data set studied by R.A. Fisher is the measurements in centimeters of four flower parts (sepal length, sepal width, petal length, and petal width) on 50 specimens for each of three species of irises (Setosa, Versicolor, and Virginica). The data are named iris in S-PLUS, and the same data can be found in R under the name iris3 (Fisher, 1936).
(a) Analyze the sepal lengths for Setosa, Versicolor, and Virginica irises, and comment on the characteristics of their distributions. (Hint: Since the data in iris and iris3 are stored as arrays, type iris3[,1,1] if using R or iris[,1,1] if using S-PLUS to isolate the sepal lengths for the Setosa irises.)
(b) Based on the analysis from part (a), construct an appropriate 95% confidence interval for the mean sepal length of Setosa irises.