When some plants are attacked by leaf-eating insects, they release chemical compounds that both repel the leaf-eaters and attract other insects that prey on the leaf-eaters. An experiment examined the release of these protective compounds by a plant that grows in the Utah desert. The investigators compared plants attacked by one of three types of leaf-eaters and other plants that were undamaged—32 plants of the same species in all, 8 per group. They then measured the emission rate of a repelling compound during seven hours. Here are the data (mean ± standard error of the mean), measured in nanograms per hour (ng/hr). Group Emission rate (ng/hr)
Control 9.22 ± 5.93
Hornworm 31.03 ± 8.75
Leaf bug 18.97 ± 6.64
Flea beetle 27.12 ± 8.62

Required:
a. Create a graph that compares the mean emission rates for the four groups. Does it appear that emissions increase when the plant is attacked?
b. What hypotheses does ANOVA test in this setting?
c. We do not have the full data set. What would you look for in deciding whether you can safely use ANOVA?
d. What is the relationship between the standard error of the mean and the standard deviation for a sample? Do the standard deviations satisfy our rule of thumb for safe use of ANOVA?
e. The test P-value is 0.207. What do you conclude?