For the studies in #6, 7 & 8 below, determine the experimental design used. Give reasons for your answer in each case.

6. A researcher conducted a study to compare the lasting quality of 3 different paints (P1, P2, P3) being considered for lane marking on highways. There were 12 sections of highway available for applying the paint. Each type of paint was randomly assigned to 4 of the highway sections. The deterioration in the paint (based on some composite measure) was to be measured after 2 years.

7. The relationship between 6 different doses of a drug that increases blood pressure and the actual amount of increase in mean diastolic blood pressure was investigated in a laboratory experiment. 12 rabbits all received, in random order, the 6 different dose levels of the drug, with a suitable interval between each drug administration.

8. A researcher studied the effects of 3 experimental diets with varying fat contents on the total lipid (fat) content in plasma. Total lipid level is a widely used predictor of coronary heart disease. 15 male subjects who were within 20% of their ideal body weight were put into 5 groups of 3 according to age. Within each the 3 experimental diets were randomly assigned to the 3 subjects. The reductions in lipid level after the subjects were on the diet for a fixed period time were recorded.