Comparative Effectiveness Research (CER) is the generation and synthesis of evidence that compares the benefits and harms of alternative methods to prevent, diagnose, treat and monitor a clinical condition, or to improve the delivery of care.

Evidence is generated through research that uses various study designs (e.g., observational, clinical trial) and synthesized through systematic reviews.

The purpose of CER, as stated by the Institute of Medicine in its 2009 report on Initial National Priorities for Comparative Effectiveness Research, is to assist consumers, clinicians, purchasers and policy makers in making informed decisions that will improve health care at both the individual and population levels.

CER addresses issues of relative effectiveness (comparing two or more tests, treatments/interventions, care delivery systems, or policies of interest). CER generally does not include placebo-controlled trials and often focuses on broader, more heterogeneous populations (i.e., "real world" populations).

The goal of CER is to provide stakeholders (patients, caregivers, providers, payers, policy makers) with information that can be used to make decisions about the benefits/tradeoffs between two or more tests, treatments/interventions, care delivery systems, or policies. As such, stakeholder engagement is often a part of the research process and the outcomes of CER should be relevant to these stakeholders. Dissemination of findings in a manner that is useful for stakeholders is also an important aspect of CER.

The Agency for Healthcare Research and Quality (AHRQ) identifies the following seven steps involved in conducting comparative effectiveness research:

1. Identify new and emerging clinical interventions.
2. Review and synthesize current medical research.
3. Identify gaps between existing medical research and the needs of clinical practice.
4. Promote and generate new scientific evidence and analytic tools.
5. Train and develop clinical researchers.
6. Translate and disseminate research findings to diverse stakeholders.
7. Reach out to stakeholders via a citizens forum.

Patient-centered outcomes research (PCOR), a term closely related to CER, is defined as "research that helps people and their caregivers communicate and make informed healthcare decisions, allowing their voices to be heard in assessing the value of healthcare options." (PCORI)

Why is CER important?

Comparative effectiveness research is designed to improve health care decision-making by providing evidence about the effectiveness, benefits and harms of different treatment options.

Although clinical trials conducted during the drug development process do provide evidence about the effectiveness of new medications, these studies are based on a small number of patients that meet a rigorous set of study entry criteria.

Both the European Medicines Agency and the FDA acknowledge the need for studies that examine the effectiveness of a drug in the 'real world'. Such studies tend to be large (to assess rare events and subgroup effects) and generalizable. They are also clinically more relevant because they address the question of which of the available treatments is best for a specific patient rather than the question whether a treatment works or not.

While these comparative effectiveness studies can be randomized studies, the great majority are not. Many rely on already collected data from large, automated healthcare databases.