J Altern Complement Med. 2002 Jun; 8(3): 385-9.

Teaching evidence-based complementary and alternative medicine: 2. A conceptual approach to causation-part 2.

Wilson K, Mills EJ, Hollyer T, Vohra S, Guyatt G.

Department of Medicine, University of Toronto, Ontario, Canada.

As noted in Part 1, of this two-part paper, one of the most common questions that arise in clinical practice is whether a causal relationship exists between two factors. In order to answer this question we noted in Part 1 that three steps need to be taken: First an association needs to be demonstrated between treatment/exposure and effect. Next, the possibility of this association being the result of error needs to be determined. Finally, additional evidence to support a cause-and-effect relationship needs to be identified. Part 1 covered the first two steps and now Part 2 describes how a complementary and alternative medicine provider goes through the last step of this process when confronted with the question of whether silicone breast implants cause the development of arthritis. Part 3 examines the importance of answering the following questions: Did the cause precede the effect? How strong was the association observed? Is increasing exposure more likely to lead to disease? Is there evidence from several different studies showing the same association? Does withdrawal of the cause result in loss of the effect? Is there a biologic model that can explain the causal relationship?