The Quantitative Environmental Learning Project reports that the second-biggest source of lead in municipal solid waste is from cathode ray tubes (CRTs), the major component of television screens and computer monitors. In a 1999 study by T. G. Townsend, a sample of discarded CRTs was tested for leachable lead concentration in milligrams per liter. The following table shows concentrations for CRTs manufactured by three companies.11

a. Does each of the columns represent a different variable? Explain.

b. Report the number of groups I and the total sample size N.

c. Use software to produce side-by-side boxplots of the three data sets.

d. Which company's CRTs appear to have the highest concentration of lead?

e. Which company's CRTs appear to have the lowest concentration of lead?

f. Which company has the least variability (spread) in lead concentrations?

g. Are the boxplots top-heavy (suggesting right-skewness) or bottom-heavy (suggesting left-skewness)? h. Report the sample standard deviations.

i. Is the rule of thumb for use of ANOVA (largest sample standard deviation not more than twice the smallest) satisfied?

j. The F statistic can be found to be 1.26, which is not very large, because the distribution is centered near 1, with area 0.05 to the right of 4. Is the P-value small or not small?

k. If standard deviations are disparate, then a smaller P-value would be needed to claim statistical significance. Do the data suggest that mean lead concentrations differ significantly for CRTs produced by the three companies?