Exercise 24 Page 197

A correlation is a relationship between data sets. We want to know if it is likely that there is a correlation between the weight of a dog and the length of its tail. Let's explore what a positive correlation between these two would lead to.

Let's look into the weight and tail length of small and of large dogs.

• A small dog typically $\text{weighs}$ $\text{little}$ and has a $\text{short}$ $\text{tail}.$
• A large dog typically $\text{weighs}$ $\text{much}$ and has a $\text{long}$ $\text{tail}.$

It is likely a positive correlation exists here. However, if a full grown dog gains extra weight this will not make its tail extend. Therefore, there is no causal relationship.