What is the relationship between per capita income in a country and child mortality? Below is computer output for three different regression models examining this relationship for countries in Central and South America. Child mortality is measured in deaths before age 5 per 1000 children born, and income is measured in U. S. dollars per person. All logarithms are base 10.

Explain why the information provided suggests that a linear model may not be appropriate for describing the relationship between child mortality and income in these countries.