<P> In other cases, two phenomena can each be a partial cause of the other; consider poverty and lack of education, or procrastination and poor self - esteem . One making an argument based on these two phenomena must however be careful to avoid the fallacy of circular cause and consequence . Poverty is a cause of lack of education, but it is not the sole cause, and vice versa . </P> <P> The third - cause fallacy (also known as ignoring a common cause or questionable cause) is a logical fallacy where a spurious relationship is confused for causation . It asserts that X causes Y when, in reality, X and Y are both caused by Z . It is a variation on the post hoc ergo propter hoc fallacy and a member of the questionable cause group of fallacies . </P> <P> All of these examples deal with a lurking variable, which is simply a hidden third variable that affects both causes of the correlation . A difficulty often also arises where the third factor, though fundamentally different from A and B, is so closely related to A and / or B as to be confused with them or very difficult to scientifically disentangle from them (see Example 4). </P> <Dl> <Dt> Example 1 </Dt> <Dd> Sleeping with one's shoes on is strongly correlated with waking up with a headache . </Dd> <Dd> Therefore, sleeping with one's shoes on causes headache . </Dd> </Dl>

A false correlation between two variables caused by a third variable