In the wonderful world of modern medicine, there are pesky little exceptions to every rule. For example, cardiologists tell us that people with high LDL (bad) cholesterol numbers are more at risk for heart attack. Yet we know that not everybody with dangerously high cholesterol levels suffers a heart attack, and not all heart attack patients have high cholesterol. In France, cardiologists puzzle over the “French Paradox” in which French citizens who eat more high-fat dairy foods, smoke more, and exercise less than all of their European neighbours have one of the lowest rates of heart disease in Europe.
This is what statisticians call intermediate or surrogate endpoints. It means you can’t really predict the final consequences based on how things are going along the way.
Consider the 2010 World Cup in South Africa for a similar illustration of intermediate endpoints. Sports pundits, for example, insist that, generally speaking, the team that can maintain possession of the soccer ball for most of the match will be the team that ultimately wins. Makes sense, doesn’t it? However, ball possession alone may not actually mean much at all to the end result. Here’s why: Continue reading