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 weighs a little and has a short tail.
A large dog typically weighs a lot and has a long 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.
