Question

Three situations are described at the start of this section, on page \(29 .\) In the third bullet, we describe an association between the amount of salt spread on the roads and the number of accidents. Describe a possible confounding variable and explain how it fits the definition of a confounding variable.

Short answer

A possible confounding variable can be 'weather conditions'. This is because weather conditions might affect both the amount of salt spread on the roads (more salt is spread in bad weather conditions) and the number of accidents (more accidents may occur in bad weather) and may trick us into believing that there's a causal link between salt quantity and number of accidents.

Step-by-step solution

Understanding the Scenario

Consider the described situation: an association between the amount of salt spread on the roads and the number of accidents.

Identifying a Confounding Variable

A possible confounding variable in this scenario might be the weather conditions. The quantity of salt spread on the roads is likely to increase with worsening weather conditions especially during winter, as salt is used to melt ice.

Explaining as Confounding Variable

Now, the increased number of accidents may not be entirely due to the amount of salt spread on the roads, but could also be a result of bad weather conditions. Here, 'weather conditions' is the confounding variable because it is related to both the proposed cause (amount of salt on roads) and the effect (number of accidents). The confounding variable, the weather condition, could be making it seem that there is a direct relationship between the amount of salt spread and the number of accidents, when indeed there might not be a direct association.