In the wake of a devastating hurricane, data collected by a relief organization showed differences in the mean amount of time that people went without power, by age, as shown in Table 13.19.

a. Describe the relationship between age and days without power shown in Table 13.19.

b. Should we conclude that age caused the length of time that people went without power after the hurricane? Explain your answer.

c. The organization mounted special outreach efforts to the elderly in response to the data. As relief workers traveled to the residences of people who lacked power, they noticed that many of the older people they visited lived in remote, rural areas with few people. One of the organization’s workers proposed entering a third variable, population density, to test whether the relationship between age and days without power still held. The reanalysis of the data indicated that the relationship worked as shown in Figure 13.27.
Explain in words what Figure 13.27 tells us about the relationship between age and days without electricity.