relation of cause and effect; causal relationship; causal link; causality
因果関係を証明するのは難しい。
It's difficult to prove a causal relationship.
事故と病気の因果関係が認められた。
A causal relationship between the accident and the illness was recognized.
因果関係がはっきりしないまま議論が続いている。
The debate continues without a clear causal relationship.