Definition: One thing is held to cause another when in fact they are both the joint effects of an underlying cause
One thing is held to cause another when in fact both are the effect of a single underlying cause. This fallacy is often understood as a special case of post hoc ergo propter hoc.
Identify the two effects and show that they are caused by the same underlying cause. It is necessary to describe the underlying cause and prove that it causes each symptom. (Cedarblom and Paulsen: 238)