What are the different types of research studies?

Comparative Effectiveness Research (CER)

Comparative effectiveness research (CER) is a direct comparison of existing options available for treating a particular medical condition. It may compare similar treatments, such as competing drugs, or it may analyze very different interventions, such as surgery and drug therapy. It may also compare the effectiveness of how and when health care is delivered, such as different intervals of follow-up, or schedules of dosing. CER can use a range of research tools and methods, including a systematic review of existing studies and evidence, modeling to simulate effects of interventions on different populations, or head-to-head clinical trials comparing one treatment to another.

There are many different types of research studies, some conducted in laboratories, and some of hospitals or clinics. Some studies are observational, while others are “experimental” and involve evaluating interventions. Each has a different design and methods, and each has its strengths and limitations. The type of research question being asked will help determine the best type of research study to conduct.

The descriptions below provide a basic overview of the different types of research studies that are used to collect evidence about breast cancer and its treatment.

Laboratory studies

Laboratory studies can be done using cells from animals or humans, or animal models. Research involving a controlled environment, such as cell cultures in a test tube or in a petri dish, are called in vitro studies. Studies done on living organisms are called in vivo studies.

Laboratory studies can also be referred to as

bench science because laboratory experiments are often conducted on a long “bench”
basic research because the studies are looking at the fundamentals of how things work and interact
preclinical research because the research is conducted prior to research in people in the clinic or in clinical trials

Human studies

There are several different types of research studies that involve humans. These include clinical trials and observational studies. Systematic reviews summarize the results from many different clinical trials and observational studies, and meta-analyses pool data collected from multiple smaller studies in addition to including a systematic review.

Clinical trials

Clinical trials are experimental studies that test new treatments in humans. Clinical trials are used to find out if new treatments work better, the same, or not as well as the standard treatment for the same disease. Clinical trials of experimental treatments (sometimes called “investigational treatments”) are conducted in a series of steps called phases.

Phase I trials include only a small number of people and are designed to test a treatment’s safety, and identify safe dosage levels and side effects.
Phase II trials include a larger number of people to test whether a treatment works (may be effective), and to further judge its safety.
Phase III trials are randomized trials that enroll hundreds or even thousands of people to test whether a drug is more effective than a placebo or than other drugs currently being used, and to monitor side effects and other information for using the new treatment safely.
Phase IV trials are also known as “post-marketing surveillance studies” and are used to monitor the long-term safety and effectiveness of a new treatment among a larger general population.

Randomization and masking are important aspects of clinical trials.

In most Phase III trials and some Phase II trials, patients are divided into at least two groups or “arms.” One group of patients gets the new treatment, and is called the “investigational group.” The treatment they get is called the “investigational treatment.” Another group of patients gets the standard treatment, and is called the “control group.” The standard treatment is the treatment you would get if you did not take part in the clinical trial. The two groups are compared to see which treatment works better. In well-designed clinical trials, patients are assigned to the different “arms” of the trial using a system similar to flipping a coin. In other words, patients do not choose whether they will get the new treatment as part of the investigational group or the standard treatment as part of the control group. Grouping patients by chance are called “randomization.”


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