Golenda et al. (1999) carried out a human clinical trial to investigate the effectiveness of a formulation of DEET (N,N-diethyl-m-toluamide) in preventing mosquito bites. The study applied DEET to the underside of the left forearm of volunteers. Cages containing 15 fresh mosquitoes were then placed over the skin for five minutes, and the number of bites was recorded. This was repeated four times at intervals of three hours. The scatter plot provided displays the total number of bites (square-root transformed) received by 52 women in the study in relation to the dose of DEET they received.

a. What feature of this study justifies our calling it an experimental study rather than just an observational study?

b. Complete the ANOVA table for these data.

c. Use the F-statistic to test the null hypothesis of zero slope.

d. Calculate the R² statistic. What does it measure?

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3 Administered dose (mg/cm²) 4 5 2 9 Square root (no. bites + 0.5) 2 000 لنا 88/ 4 5