13.16 Ecological effects of pharmaceuticals on fish. Drugs used to treat anxiety persist in wastewater effluent, resulting in relatively high concentrations of these drugs in our rivers and streams. To understand the impacts of these anxiety drugs on fish, researchers commonly expose fish to various levels of a drug in a laboratory setting and observe their behavior.11 In one 2 × 2 experiment, researchers considered exposure to oxazepan through the water (Y/N) and through the diet (Y/N). Ten one-year-old perch were assigned to each of the four treatment combinations. After seven days of exposure, each fish was observed for activity. This was recorded as the number of swimming bouts (defined as movement exceeding 3.5 cm) over a 10-minute period.

  1. (a) The response is the number of movements in 10 minutes, which can only be whole number. Should we be concerned about violating the assumption of Normality? Explain your answer.

  2. (b) Construct an interaction plot and comment on the main effects of exposure through diet and water and their interaction.

  3. (c) Analyze the count of swimming bouts using analysis of variance. Report the test statistics, degrees of freedom, and P-values.

  4. (d) Use the residuals to check the model assumptions. Are there any concerns? Explain your answer.

  5. (e) Based on parts (c) and (d), write a short paragraph summarizing your findings.