A species of Caribbean mosquito is known to be resistant against certain insecticides. The effectiveness of five different types of insecticides—temephos, malathion, fenitrothion, fenthion, and chlorpyrifos—in controlling this mosquito species was investigated in the Journal of the American Mosquito Control Association (March 1995). Mosquito larvae were collected from each of seven Caribbean locations. In a laboratory, the larvae from each location were divided into five batches and each batch was exposed to one of the five insecticides. The dosage of insecticide required to kill 50% of the larvae was recorded and divided by the known dosage for a susceptible mosquito strain. The resulting value is called the resistance ratio. (The higher the ratio, the more resistant the mosquito species is to the insecticide relative to the susceptible mosquito strain.) The resistance ratios for the study are listed in the next table (top of p. 545) and saved in the MOSQUITO file. The researchers want to compare the mean resistance ratios of the five insecticides.

a. Explain why the experimental design is a randomized block design. Identify the treatments and the blocks.

b. Conduct a complete analysis of the data. Are any of the insecticides more effective than any of the others?