A series of observational studies revealed that people who typically consume 3 servings of whole grain per day have about a 20% lower risk of dying from heart disease and about a 15% lower risk of dying from stroke or cancer than those who consume no whole grains.

a. Explain how confounding makes it difficult to establish a causeand- effect relationship between whole grain consumption and risk of dying from heart disease, stroke, or cancer, based on these studies.

b. Explain how researchers could establish a cause-and-effect relationship in this context.