In a clinical trial, the endpoints are the things that you measure to determine whether a treatment is effective. For example, if your trial is testing whether a new drug reduces blood pressure, then reducing blood pressure would be an endpoint of interest. In theory, any measurable value could be used as an endpoint for a clinical trial. However, there are two different types of endpoints: objective endpoints and subjective endpoints. The difference between these two categories may seem obvious at first glance; however there are many subtle nuances that can affect your study’s results.
Objective endpoints are easier to collect and measure
Objective endpoints are usually easier to measure, collect, analyze and interpret because they rely on measurable physical or behavioral changes. Examples include blood pressure, heart rate, oxygen saturation levels and body temperature. In contrast, subjective endpoints are usually more difficult to collect and assess because they require verbal reports from the patient or caregiver. Examples include pain scores or quality of life assessments.
Subjective endpoints, while harder to measure and assess, may be more clinically meaningful
As discussed previously, the assessment of subjective endpoints is challenging for a variety of reasons. Training investigators in the proper assessment of subjective endpoints helps in ensuring that trial results are reliable and reproducible. Subjective assessments require that participants or patients be examined by a clinician or investigator who can answer questions about the patient’s health status and experience during treatment. For example: “Do you feel better today? How do you feel on this scale between 0 and 10?” While these questions are relatively straightforward when asking an individual patient with no other confounding factors (e.g., age), studies with multiple participants will likely have difficulty aggregating subjective data into meaningful measures without blinding clinicians or researchers from results—something that is difficult in most trials due to cost and logistical barriers. However, despite challenges utilizing subjective measurements in clinical trials, they remain an important component in many areas of medicine including pain management and mental health treatment where quality-of-life improvements can be difficult to measure objectively but critically important to those affected by illness or injury.
Biomarkers are objective endpoints, but not all objective endpoints are biomarkers
Biomarkers are objective endpoints. They are quantitative measures of a biological process, and therefore easier to measure than subjective clinical endpoints. However, not all objective endpoints are biomarkers. Although many objective clinical outcomes could be used as biomarkers, some are not considered clinically meaningful because they do not correlate well with patient-reported outcomes that matter most to patients and physicians (e.g., relief from pain).
For some endpoints, like pain, it may not be possible to tell the difference between objective and subjective
Pain is a subjective endpoint because it is difficult to measure and can only be reported by the patient. Pain is an example of an endpoint that is not objective, but it may be possible to determine whether there was less pain in one group more than another, even though this would not be confirmed objectively.
Both objective and subjective endpoints can be useful in clinical trials.
Objective endpoints are generally the easiest to measure, but they don’t always capture what patients experience. Objective measures of clinical outcomes can include analyzing blood levels, changes in biomarker expression, or other biological changes that are observable or measurable. Subjective clinical outcomes can include patient-reported assessments like pain scores or overall quality of life.
Subjective endpoints (also called “patient-reported outcomes”) are not always the same as objective ones—a change in a person’s self-reported symptom level might not be reflected by an observable physical marker such as a blood level measurement. A patient may report feeling less pain on a scale of 1–10 even though they have no physical signs of improvement.
Both types of endpoints have their place in clinical trials. As we’ve seen above, objective endpoints are generally easier to collect and measure than subjective ones, but they don’t always give us as much information about how patients feel about their symptoms. Subjective endpoints can be more meaningful to patients because they capture a sense of how well their life has improved since taking your drug or device—but they can also be biased by what the patient thinks he or she should expect from treatment.
So which type of endpoint should you use? It depends on your goals for the study and what kind of data would be most useful for supporting those goals (e.g., enrollment targets or regulatory decision-making). But whatever kind of endpoints you choose, make sure that they meet these criteria: reliable and reproducible; clinically relevant; sensitive enough to detect an expected difference between groups; not affected by other factors such as disease severity or comorbidities.