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National Information Center on Health Services Research and Health Care Technology (NICHSR)

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Introduction to Health Services Research : A Self-Study Course

Module 6: Basic Components of a Study (Page 8 of 11)

Surveys | Cohort Studies | Case-Control Studies | Randomized Clinical Trials

Strengths and Pitfalls: Randomized Clinical Trials (RCTs)

RCTs follow two groups of people over time to see who achieves a particular result. In this case, the researchers assign or randomize the people to their groups. This randomly assigning people to a group is called randomization or random assignment.

If this is done properly, each person has an equal chance of being assigned to either group, reducing the possibility of the groups having different features. Each group receives a different intervention. For example, Group 1 gets a real medicine and Group 2 gets a placebo. No one knows who gets what. This is called masking.

Researchers want to know if Group 1 will do better than Group 2. When the study period ends, the researchers evaluate their different outcomes and calculate the risk of one group developing the result compared to another.

For example, researchers randomize workers to receive indemnity insurance or managed care coverage. They watch people over time and measure their utilization of health services. They compare the groups to evaluate whether the type of insurance coverage influenced their use of medical care.

In clinical experiments, investigators randomize patients with the same disease, such as hypertension, to two different drug groups. One may receive an experimental medication while the other receives a placebo. The researchers measure the effect of the drugs on the hypertension.

Advantages

Controlled clinical trials hold the advantage in assessing causality.

Randomization produces comparable study groups that should only differ in the intervention given. People start off the same and have an equal chance of receiving the treatment or not. Researchers control the people’s experiences very carefully so you are sure that it’s the treatment that makes the difference!

Therefore, differences in outcome can be attributed to that intervention, such as a drug, and the researchers can conclude that the intervention caused the results. Since the people are similar in the beginning of the study, researchers can be confident that the intervention precedes the effect, a major determinant of causality.

Disadvantages

However, clinical trials are not perfect. They are expensive and time-consuming. Biases may render their results less reliable. For example, if study participants or researchers know their group assignment, they may expect a particular result. Masking study participants and researchers avoids treating people differently based on the intervention. Losing participants along the way may also jeopardize the results. Did people leave the study because the treatment was too harsh or for reasons unrelated to the study?

While randomized clinical trials can prove causality, ethical considerations usually limit their utilization. Randomizing participants into smoking and non-smoking arms of a study to detect lung cancer would provoke an uproar among scientists and the public. For these reasons, many investigations must be observational in which groups of naturally occurring behaviors are followed and measured.

Remember also that clinical trials occur under very specialized, controlled conditions that do not represent everyday life. Therefore, the results obtained in this environment may not transfer to larger groups of people not engaged in research.

Exercise

  1. What are the search terms that you might use to extract this kind of study when searching using PubMed?
  2. Occasionally researchers delve into unusual topics. This is often a thrill for librarians who are helping them retrieve citations for their research. If you were asked to find out what kind of publications were coming out on the topic of randomized clinical trials, what would you expect to find? The linked search contains citations for you to examine on published randomized controlled trials.
  3. Why do results obtained under very specialized, controlled conditions may not transfer to larger groups of people not engaged in research?

Discussion Questions

  1. Now that you've gone through the content in this module why do you think it's necessary for librarians to know something about study design?
  2. Where (what sources) would you start to locate additional information about study design? (Hint: Look at the Enrichment Section for this module but also retrieve other content from the Web).
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