Is there an association between level of happiness and the risk of heart disease? Researchers studied 1739 people over a 10 year period and asked questions about their daily lives and the hassles they face. The researchers also determined which individuals in the study experienced any type of heart disease. After their analysis, they concluded that happy individuals are less likely to experience heart disease.
(a) What type of observational study is this? Explain.
(b) What is the response variable? What is the explanatory variable?
(c) In the report, the researchers stated that "the research team also hasn't ruled out that a common factor like genetics could be causing both the emotions and the heart disease." Use the language introduced in this section to explain what this sentence means.