An endpoint, or its synonyms as interest factor and endpoint (English outcome), is a measurable indicator that the researcher assumes it will be modified by therapeutic innovation or action health prevention as part of a randomized controlled trial. There may be health indicators (clinical, biological, psychological, socio-professional and / or survival), quality of life (generic and / or specific), security (benign and / or serious incidents) or utility (cost / effectiveness, cost / benefit). The quality of the endpoint and the tool to be measured is critical to identify a change. Effective intervention may mistakenly not be demonstrated by choosing the wrong endpoint (eg some variable factor in time) or a tool not sensitive enough. This choice must be supported by a thorough biographical research.
A difficult choice
The design of a randomized controlled trial systematically raises the question of the choice of the primary endpoint. This choice determines the a priori calculation of the number of participants in each group it will take to verify the effectiveness of a therapy or a health care prevention. The numbers have to be adapted to the size of the expected effect to ensure adequate power. Over the desired effect, the smaller the number of subjects required to be important. This calculation is based on a supposed effect and a level of statistical power. In a given (size of the desired effect and base frequency of the event) context, the power depends only on the number of subjects (Cucherat, 2013). The calculation requires knowing or making assumptions about the parameters on the power: basis risk, size of the effect to highlight, alpha risk (typically 5%) and desired (usually 90%) power. The primary endpoint can be diverse, ranging from a biological marker of the quality of life, through the behavior (weekly physical activity, adherence) and a medico-economic indicator (care utilization, consumption of health, emergency hospital admissions, days off work …).
What it means for Users
Randomized controlled trials do not measure the persistence of symptoms and quality of life systematically. Yet in the case of chronic disease where cure is not possible, these endpoints are central in terms of the patient. Blog in Health regularly address this issue.
What it means for Health Professionals
Reading a randomized controlled trial deserves the most attention about the primary endpoint. It is supposed to be changed by the innovation tested. Sometimes studies show statistically significant on secondary outcomes, not the main criterion effects. Interpretation of the results is then subjected to debate.
What it means for Researchers
Randomized controlled trials are published with a population below the required number of subjects initially planned. The authors regret not being able to achieve the expected power. These deficiencies make it almost futile efforts by agencies involved in the research and development of an innovation. The choice of the primary outcome should be well thought out.
What it means for Policymakers
The prevailing logic in the choice of the primary endpoint in a randomized controlled trial is crucial in determining the number of subjects required for the study. It can be debated, from a purely medical model patient-centered (so important for therapists) to a vision of society (so important for funders of the health system). The therapist will be more attentive to the survival, persistence of symptoms, health status or quality of life. Relatives will pay more attention to the emotional state and behavior of the patient. Social security and mutual focus greater attention to the use of care. Social Security and communities will listen using social benefits. Finally, the employer will be more vigilant about returning to work.
Cucherat M (2013). Site web.
To reference this Blog en Sante © article.
Ninot G (2014). Definition of endpoint. Blog en Sante, L8.
© Copyright 2014 Grégory Ninot. All rights reserved.