1.19 Internet use and life expectancy: The following scatterplot was created as part of a study evaluating the relationship between estimated life expectancy at birth (as of 2014) and percentage of internet users (as of 2009) in 208 countries for which such data were available.
b) What type of study is this?
c) Which of the following variables can be considered as a possible confounding variable that might explain the above relationship?