Question 6.38

image 3. Figure 6.23 is a scatterplot of data from the World Bank. The individuals are all the world’s nations for which data are available. The explanatory variable is a measure of how rich a country is, which is the gross domestic product (GDP) per person. GDP is the total value of the goods and services produced in a country, converted into dollars. The response variable is life expectancy at birth. Three African nations are outliers, with lower life expectancy than usual for their GDP. A full study would ask what special circumstances explain these outliers.

  1. Describe the direction and form of the relationship. Aside from the outliers, it is moderately strong.
  2. Explain why the direction and form of this relationship make sense.
image
Figure 6.23: Figure 6.23 A scatterplot of the life expectancy of people in many nations against each nation’s GDP per person, for Exercise 3.

3.

(a) Life expectancy increases with GDP in a curved pattern. The increase is very rapid at first, but it levels off for GDP above roughly $5000 per person.

(b) Sample response: As countries go from very poor to moderate economies, improvements in quality/ quantity of food, housing, and medical care have a great impact on increasing life expectancy. As countries move from moderate economies to rich economies, such improvements still improve life expectancy but at a lower rate.