Researchers from the Department of Oceanography at Texas A&M University gathered data on ages (in millions of years) of fish fossils gathered at two sites and at various depths (in meters below sea floor, mbsf).

a. We may think of the age of a fossil as determining how deep it will be, or we may think of the depth of a fossil as providing information about its age. Based on the way the scatterplots have been constructed, which has been taken to be the explanatory variable, age or depth?

b. We may also consider the third variable, site. Tell whether it is explanatory or response, and whether it is categorical or quantitative.

c. Based on the appearance of the scatterplots, does the relationship between age and depth appear stronger at the first or the second site?

d. The scatterplot on the right shows the relationship between ages and depths for both sites combined. Does the appearance suggest it is better to study the sites separately or combined? Explain.

e. If we do inference about age based on depth of fossils, should we consider the population to be all fish fossils at any site or all fish fossils at the site from which the sample was obtained?