Not all research studies are created equal and that’s on purpose. But the study type is a key component that should be used when assessing the importance and potential impact of research.
A study of two people is going to yield less widely applicable insights than a study of 2,000. So when you read the latest headline about a diet that can prevent cancer or a dye that can cause it, take a look at the kind of study it was to help gauge the importance of its findings.
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Here is a rundown of some of the most common types of research studies behind the health headlines, from observational studies to experimental trials. Having a better understanding of how a study is conducted can help you understand its advantages and limitations.
In an observational study, researchers do not intervene; they simply observe study subjects to determine whether there’s a correlation between an exposure and disease risk within a given population. Such studies fall into the category of epidemiological research, which aims to understand the causes, or risk factors, of disease and how they can be modified or prevented. Results of such studies can help guide and inform prevention research.
Depending on their study design, observational studies can be prospective (forward-looking) or retrospective (backward-looking).
Experimental studies, also called randomized, controlled trials, or RCTs, assign groups of people at random, like the toss of a coin, to either receive (or not receive) a preventive or therapeutic intervention or screening test, such as a drug, device or procedure. Researchers then assess the impact of the intervention on those who received it as compared to those who did not.
Well-known examples of RCTs include those conducted by the Women’s Health Initiative, a massive nationwide undertaking coordinated by Fred Hutchinson Cancer Research Center. Launched in 1991 with a $625 million grant from the National Heart, Lung, and Blood Institute, the WHI conducted four randomized, controlled Phase 3 trials (see below re: trial phases) that were designed to measure the effects of various interventions, from hormone therapy to dietary supplements to a low-fat diet, on preventing the most common health issues in postmenopausal women, including heart disease, breast and colorectal cancer, and osteoporosis-related fractures. The initiative, which enrolled more than 161,000 older women across the U.S., had — and continues to have — a wide-ranging impact on medical practice and women’s health.
RCTs are designed to evaluate the safety and effectiveness of experimental drugs or tests for diseases such as cancer. They are conducted incrementally, in a series of steps that are called phases. Below are brief descriptions of the study phases.
When reading about study results, it is important to not confuse causation with correlation or association. While prospective, observational studies that follow large groups of people over time can suggest relationships between certain exposures and diseases, they cannot on their own prove cause and effect. Only randomized, controlled trials comparing intervention and control groups — the research gold standard — can definitively confirm causation.
The bottom line: Always interpret health headlines — particularly nutrition claims — with a proverbial grain of salt, because if they seem too good to be true, they probably are.
Kristen Woodward, a former associate editor at Fred Hutchinson Cancer Center, had been in communications at Fred Hutch for more than 20 years. Before that, she was a managing editor at the University of Michigan Health System and a reporter/editor at The Holland Sentinel, a daily in western Michigan. She has received many national awards for health and science writing. She received her B.A. in journalism from Michigan State University.
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