In New York State, the winter months produce higher heating bills and higher levels of depression. Although the numbers show that higher heating bills are related to higher levels of depression, what is the most likely explanation for this relationship?

Answer: Third variable problem

Explanation: The third variable problem occurs when a causal relationship or correlation is mistakenly observed between two variables. The observed correlation shown between these two variables is caused or associated with a third variable usually called a confounding, lurking or third variable rather than underlying relationship between the two variables.

In the scenario above, the positive correlation obved between heating bills and level of depression is not due to an underlying relationship between both variables but a confounding variable variable leading to the observed causal relationship.