Use the data in AllCountries to answer the following questions.
(a) Is the number of mobile subscriptions per 100 people, Cell, a significant single predictor of life expectancy?
(b) Explain why GDP (per-capita Gross Domestic Product) is a potential confounding variable in the relationship between Cell and LifeExpectancy.
(c) Is Cell a significant predictor of life expectancy, even after accounting for GDP?

Data in AllCountries

Information about 213 individual countries as determined by the World Bank in 2008 (or later).
Country ........................Name of the country
Code .............................Three letter country code
LandArea ......................Size in sq. kilometers
Population ....................Population in millions
Energy ...........................Energy usage (kilotons of oil)
Rural ..............................Percentage of population living in rural areas
Military ..........................Percentage of government expenditures directed toward the military
Health ...........................Percentage of government expenditures directed towards healthcare
HIV ................................Percentage of the population with HIV
Internet ........................Percentage of the population with access to the Internet
Developed ...................Categories for kilowatt hours per capita, 1 = under 2500, 2 = 2500 to 5000, 3 = over 5000
BirthRate .....................Births per 1000 people
ElderlyPop ...................Percentage of the population at least 65 years old
LifeExpectancy ............Average life expectancy (years)
CO2 ..............................CO2 emissions (metric tons per capita)
GDP ..............................Gross Domestic Product (per capita)
Cell ...............................Cell phone subscriptions (per 100 people)
Electricity .....................Electric power consumption (kWh per capita)