Question

Describe an association between two variables. Give a confounding variable that may help to account for this association. Air pollution is higher in places with a higher proportion of paved ground relative to grassy ground.

Short answer

Urbanization is a confounding variable that might help explain the association between air pollution and the proportion of paved ground relative to grassy ground. This is because urbanization increases both air pollution and the proportion of paved surfaces, potentially contributing to the observed correlation.

Step-by-step solution

Comprehend the Association

Understand the stated correlation and causation. The association here is that air pollution (variable 1) increases with increasing proportion of paved ground relative to grassy ground (variable 2). This understanding is important to correctly identify a suitable confounding variable.

Consider Possible Confounding Variables

Identify external factors that impact both variables in the stated association. A confounding variable might influence both the air pollution levels and the ratio of paved to grassy ground in the same direction. For example, urbanization could be such a variable. As cities expand, they tend to have more paved grounds and less grassy areas, and they also tend to produce more air pollution due to increased human activities and vehicle operations.

Choose Appropriate Confounding Variable

After exploring various potential confounding variables, select the most suitable one. Here, urbanization can be chosen as the confounding variable because it extensively influences both air pollution and the proportion of paved ground to grassy ground by forming the backbone of the observed correlation.