CER compares two or more care options (e.g. treatments, prevention measures, diagnostic tools) to determine which work best, for whom, and in what circumstances.
For an example, a CER study might compare joint replacement surgery with a new drug in treating severe osteoarthritis of the knee. Researchers would examine the benefits as well as the disadvantages of both options. The study would generate evidence with relevance for different subgroups, such as women under age 65 or overweight men.
CER is of great benefit to those who are not well-served by typical studies, such as children, the elderly, seriously and terminally ill patients, and minorities. CER studies are capable of generating evidence that can contribute substantially to personalized care.
With increasing cost pressures on health care, knowing which care option are most effective for which people is more important than ever.
Conventional studies usually compare treatments to placebos and seldom look at complex strategies, such as the combination of medication, exercise, and diet to treat cardiovascular disease. CER studies are different. They compare treatment options to one another, examining both the benefits and harms. They are very well suited for evaluating complex strategies.
Patients in most conventional research studies resemble one another. Those who have more than one medical condition or are taking multiple medications are typically eliminated. CER, on the other hand, uses a broad methodology and deviates from the strictly controlled trial framework by adjusting design elements, such as eligibility criteria.
CER places a strong emphasis on involving stakeholders (e.g. patients, health care providers). Unlike conventional research practices, CER identifies the kind of evidence stakeholders want and establishes research priorities and protocols accordingly.
The old paradigm of clinical research can be likened to passengers on a city bus. The passengers are being driven from point to point, sometimes bypassing or falling short of their destinations. These anonymous participants have no say about the route, the speed, or their fellow passengers.
CER offers a new paradigm with a different metaphor: The car pool. Each participant brings unique skills, perspectives, resources and a personal sense of urgency about getting to a specific destination.
On the bus, it doesn’t matter how urgent things are for you. You arrive when the bus arrives. The stop may or may not be close to your destination. In the car pool, each member drives, offers direction, and contributes personal knowledge and experience.
Comparative effectiveness research has the potential to put patients in the driver’s seat, or at least share the driver’s seat with other stakeholders. When properly designed, CER offers new evidence, insight into subgroups, and timely, relevant results.
This type of research excludes as many complicating influence factors as possible. A good example is the typical drug study, such as a comparison of a new drug to reduce high blood pressure with a placebo or another drug, in patients with no other medical problems and who are reminded frequently to take all of their study medications.
When we measure effectiveness, we are trying to answer the question: Did this treatment work in a real-world setting, similar to how health care would usually be delivered and used?
The key question in this approach is to determine which treatment works best for which patients, and under what circumstances. A good example of an effectiveness study is a study that compares a drug with an exercise program to reduce high blood pressure in patients treated by community physicians.
To have a clear picture about the clinical evidence for an intervention, both efficacy and effectiveness are relevant. However, as its name clearly implies, comparative effectiveness research focuses on developing evidence of effectiveness. And it often involves comparing at least two widely used treatment options, since those are the type of choices that patients and doctors commonly face.
Understanding the distinction between efficacy and effectiveness in clinical studies is critical to our understanding of CER, and relates directly to the purpose of CER as described by the Institute of Medicine, to assist decision makers in making informed decisions.
Three elements of study design influence the placement of each study within the efficacy effectiveness continuum:» Eligibility criteria of study participants
Let’s examine each of these in detail:
The eligibility criteria of the study participants. For example, a study which included only highly selected patients of younger age without co-morbidities and co-medication who are expected to have a better reaction to the intervention would fall on the efficacy side of the continuum. Maximum effectiveness would mean to include all types of patients who are affected by the disease without excluding subgroups of patients with risk factors e.g. high blood pressure, which might predict a less favorable response to the treatment.
The treatment protocol. A study in which a very standardized treatment protocol as study intervention (e.g., a fixed exercise program without any flexibility) would fall on the efficacy side of the continuum. Maximum effectiveness would suggest a flexible treatment protocol as implemented in routine or usual care (e.g., exercise program individually adapted to the age and co-morbidities and preferences of the patient).
The outcome measures. Objective outcome measures such as death and laboratory data would fall on the efficacy side of the continuum. Maximum effectiveness would rely more heavily on patient-reported outcome measures (e.g., symptom scales or quality of life measures).
When study participants are highly selected, the treatment is standardized, and all major outcomes are not directly experienced by patients, such a study would provide information on efficacy more than effectiveness.
In this case, the study results would be very valid for similar patients in similar settings, but less so when applied under other conditions. Thus the study is said to have a higher internal validity. This means that the results of the study are less influenced by other factors, for example, beliefs and health behaviors. We may reasonably conclude that the results actually represent the effect of the treatment we have researched.
However, when study participants represent a mixture of typical patients, the treatment protocol is more flexible, and the outcome measures are more patient-centered or subjective, the study measures effectiveness more than efficacy. When the study measures effectiveness, the results are regarded as more relevant to real-world health care decisions. In other words, this study is considered to have a higher external validity.
It's important to keep in mind that CER does not only mean doing studies that represent the extreme range of effectiveness studies. The “art” of CER requires that researchers deliberately sacrifice some degree of internal validity in order to increase the generalizability, relevance, feasibility and timeliness of research results. The right balance of the desirable features of research cannot be determined rigorously through a scientific process. The optimal balance emerges from the process of engaging stakeholders in a discussion about each element of study design, in light of current evidence, and what sorts of decisions must be made.