Explanation

Patients, health professionals, and researchers may have different views about which potential outcomes of a health action are important. Fair comparisons often do not include all the outcomes that are important to everyone. For example, they might only have measured what happened a short time after the health action, but what happens after a longer time may matter more to some people and short-term outcomes may not reflect long-term outcomes. Or, researchers might have used a substitute (surrogate) outcome that is easy to measure – like a change in a blood test – rather than an outcome that matters to patients – like feeling sick. One reason for studies measuring surrogate outcomes rather than patient-important outcomes is the preference of researchers and funding agencies to obtain results faster, with fewer patients and at lower costs.

Researchers have found that studies that measured substitute outcomes reported larger treatment effects than studies measuring outcomes that were important to patients. When researchers use a less important outcome as a substitute for a more important outcome, we cannot be sure that the effect on the important outcome will be the same as the effect on the substitute outcome. In the absence of patient relevant outcomes, it is important to consider whether substitute outcomes predict important benefits and harms.

It is sometimes important to consider outcomes that are important to other people besides the person being treated. For example, the use of antibiotics may increase antibiotic resistance, and not being vaccinated for Covid-19 or not avoiding contact with other people may increase the risk of infection for others. When decisions are made for a group of people rather than for individuals, the outcomes that are important to anyone who is affected should be considered.

Remember: The outcomes that are important for a decision may not have been measured in research. Using substitute outcomes to inform a decision can be misleading.