How Do We Know What’s Responsible for Illness?

Dr. Kathryn Fox, an Australian medical doctor and forensic thriller author, highlights the difficulty in distinguishing between correlation and causation in medicine. While patients often seek clear answers for illnesses—such as headaches after buying a new phone or starting a job—linking two events does not prove causation. Human intuition often assumes proximity in time means one event caused another, but science requires deeper investigation. The relationship between smoking and lung cancer serves as a key example. Initially, smoking was widely promoted as healthy, even by doctors, but researchers later observed a correlation between smoking and higher lung cancer rates. To establish causation, scientists examined whether cigarette smoke contained carcinogens, compared cancer rates among heavy and light smokers, and tracked trends across different populations. Over time, declining smoking rates aligned with falling lung cancer rates, reinforcing the link through extensive peer-reviewed evidence. Fox cautions against drawing conclusions about modern factors like mobile phones, processed food, or social media based solely on timing. For instance, rising autism rates coincide with the decline of asbestos, leaded petrol, and smoking, yet no evidence suggests these decreases caused autism. Without rigorous, multi-faceted studies, assumptions about causation can be misleading. The process of determining causation in medicine resembles detective work, requiring multiple lines of evidence before reaching a confident conclusion. Fox stresses that a single study or observation is insufficient—only consistent, large-scale research can reliably identify true causes of disease. Public understanding of health risks must be grounded in scientific rigor, not instinctive pattern recognition.