Final answer:
A common cause relationship occurs when two variables are both influenced by a third variable. For example, ice cream sales and sunglasses sales may increase on hot and sunny days. However, the increase in one variable does not directly cause the increase in the other variable, as they are both influenced by the shared third variable, the weather.
Step-by-step explanation:
A common cause relationship occurs when two variables are both influenced by a third variable. For example, let's consider the relationship between ice cream sales and sunglasses sales. Both of these variables may be influenced by a third variable, such as the weather. On a hot and sunny day, people are more likely to buy ice cream and sunglasses, creating a positive correlation between the two variables. However, the increase in one variable does not directly cause the increase in the other variable, as they are both influenced by the shared third variable, the weather.