A headline in a recent edition of USA Today stated, Attending religious services lowers blood pressure more than tuning in to religious TV or radio, a new study shows.

The study referred to was conducted by the U.S. National Institutes of Health. The study followed 2,391 people aged 65 or older for 6 years. The article described one of the studys principal findings: People who attended a religious service once a week and prayed or studied the Bible once a day were 40% less likely to have high blood pressure than those who dont go to church every week and prayed and studied the Bible less.

(a) Explain how you know this study is observational rather than experimental.

(b) What is the response variable in this study?

(c) What is the (implied) explanatory variable?

(d) Identify two plausible confounding variables, and explain how these variables might distort the relationship between the explanatory and the response variable.