Lecture 4.0 Causality 1 (2024) (1).pptx

Evidence based Medicine Causality Prof Haroon Saloojee Delivery objectives Differences between association and causation Criteria for establishing causality Threats to study validity Bias Confounding Chance Do you agree? Cigarette smoking causes lung cancer...

Evidence based Medicine Causality Prof Haroon Saloojee Delivery objectives Differences between association and causation Criteria for establishing causality Threats to study validity Bias Confounding Chance Do you agree? Cigarette smoking causes lung cancer HIV causes AIDS Certain tampons cause toxic shock syndrome Use of cell phones causes brain cancer Eating a high-carbohydrate diet promotes diabetes Air pollution causes asthma Zika virus causes microcephaly SARS-Cov2 causes Covid-19 The concept of cause The cause of a disease is an event, condition, characteristic, or a combination of these factors which plays an important role in producing the disease. Logically, a cause must precede a disease. Remove exposure and some cases do not occur (disease rate drops) Do not need to understand all causal factors to prevent disease (e.g. lung cancer and smoking)  “Everyone says that smoking causes cancer, but we can't really say that, can we?” “There is an association between smoking and cancer, but we know that association does not imply causation, don't we?” When does association imply causation?  Association vs. Causation Association is simply an identifiable relationship between an exposure and disease e.g., Rotavirus is isolated more frequently from children with diarrhoea than those without Implies that exposure might cause disease Exposures associated with a difference in disease risk are often called "risk factors" Association vs. Causation Causation implies that there is a true mechanism that leads from exposure to disease e.g. long-term heavy smoking causes myocardial infarction Finding an association does not make it causal e.g. hospital stays are associated with an increased mortality rate, but this does not mean that hospitalisation cause death MCQ What is Association refers to a relationship between two variables, while causation indicates a cause-and-effect relationship the main between them. differenc Association and causation are two terms used interchangeably e to describe the same concept. between associati Association is a weaker form of causation, suggesting a on and possible relationship, while causation indicates a strong and causatio proven cause-and-effect relationship. n? Association and causation are two different terms that describe unrelated concepts. History In 1964, the US Surgeon General's report on smoking implicated tobacco as a cause of lung cancer. This ignited a tremendous controversy. Bradford-Hill, advanced standards that could be used to judge when an association might be causal. The Bradford-Hill criteria Strength Is the risk so large that we can easily rule out other factors? Consistenc Have the results been replicated by different researchers y and under different conditions? Specificity Is the exposure associated with a very specific disease as opposed to a wide range of diseases? Temporalit Did the exposure precede the disease? y Biological Are increasing exposures associated with increasing risks gradient of disease? Plausibility Is there a credible scientific mechanism that can explain the association? Coherence Is the association consistent with the natural history of the disease? Experiment Does a physical intervention show results consistent with al evidence the association? 1. Strength of Association Strong associations are less likely to be caused by chance or by bias A strong association is one in which the relative risk is: high (>1), or low (