2. Observational studies have suggested that daily intake of Vitamin E is associated with a lower risk of heart disease. Yet, carefully designed double-blind randomized experiments have shown that vitamin E has no effect in reducing risk of heart disease. a) For each study (observational and experiment), what are the response and explanatory variables and treatments? [2 marks] b) Outline the design of each study on a diagram [2 marks] 0) For the observational study, identify a lurking variable that may explain the association between Vitamin E intake and risk of heart disease? Explain why your answer satises the denition of a lurking variable. (Hint: What can you say about people who regularly take Vitamin E supplements?) {2 marks] 2. Observational studies have suggested that daily intake of Vitamin E is associated with a lower risk of heart disease. Yet, carefully designed double-blind randomized experiments have shown that vitamin E has no effect in reducing risk of heart disease. a) For each study (observational and experiment), what are the response and explanatory variables and treatments? [2 marks] b) Outline the design of each study on a diagram [2 marks] c) For the observational study, identify a lurking variable that may explain the association between Vitamin E intake and risk of heart disease? Explain why your answer satisfies the definition of a lurking variable. (Hint: What can you say about people who regularly take Vitamin E supplements?) [2 marks]