Cause associations can also be classified as direct or indirect. A direct cause associations (or direct cause) can be thought of as representing a causal pathway in which there are no intermediate steps, while an indirect cause direct cause(or indirect cause) involves one or more intervening factors. For example, in a direct causal association, X causes Y, where X is the causative exposure, and Y is the outcome. In an indirect cause direct cause, I causes X, which in turn causes Y. while I is a direct cause of X, it is an indirect cause of Y. since I causes X, and X causes Y, it follows that I causes Y based on the definition of cause. A change in I will result in a change in X, which in turn will result in a change in Y. thus, I is an indirect cause of Y.
Indirect cause can include a variety of predisposing or enabling factors that precede the direct cause. For example, excessive heat applied to the skin is the direct cause of burns, but the exposure to the heat may be influenced by a dangerous working environment or failure to follow certain safety precautions, which might be considered indirect causes of burns. Also, the human immunodeficiency virus (HIV) is said to be the direct cause of AIDS, but factors that facilitate contraction HIV include sharing syringes and promiscuous sexual behaviors. In practice, controlling the predisposing or enabling factors should result in a decrease in the outcome. Predisposing or enabling factors are often referred to as risk factors, which, as noted previously, may or may not be causal in nature. When used in connection with indirect causes, it is assumed that they represent causal factors.
Whatever classification scheme is used, most health-related problems can be determined to have multiple causes. This multifactorial etiology, which has been referred to often in this text, presents a challenge to epidemiologists who are concerned with unraveling the determinants of disease and to the health professionals whose efforts are directed toward disease prevention and control, the models of causation and the methods of intervention will continue to undergo change.