A recent study has found an association between elevation and lung cancer incidence. Incidence of cancer appears to be lower at higher elevations, possibly because of lower oxygen levels in the air. We are told that “for every one km rise in elevation, lung cancer incidence decreased by 7.23” where cancer incidence is given in cases per 100,000 individuals.

(a) Is this a positive or negative association? 

(b) Which of the following quantities is given in the sentence in quotes: correlation, slope of regression line, intercept of regression line, or none of these? 

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