Randomized Clinical Trial

A randomized clinical trial is a research design regarded as the highest level of evidence in assessing the outcome and effect of therapeutic interventions. Such trials are prospective studies that evaluate the short-term or longitudinal outcomes of two groups. Both groups are selected randomly and properly allocated to treatment groups; thereby, distributing equally any preexisting confounds that can affect the outcome of interest. Theoretically, characteristics of the allocated groups at baseline are considered the same before the trial commences and differences observed between the two groups following treatment intervention at the end of the trial are likely to be attributed to the type of treatment administered. Design issues are many, but proper blinding techniques, randomization, exclusion/inclusion criteria, and measures to minimize attrition are paramount.

Two main types of randomized clinical trials are performed and are known as the crossover design and the parallel design. The latter entails two independent groups, a control group and an intervention group, who receive two different treatments and are observed through a specified time interval and their outcomes [Page 1469]are noted. Conversely, a crossover design represents two paired groups that receive the same treatment at one point or another, but at alternating times. In the crossover design, the main interest is to measure the treatment effect and determine the existence of a sequential or period effect.

Randomized clinical trials are prospective studies that evaluate the short-term or longitudinal outcomes of two groups.

Also, concern rests with any residual or carry-over effect the previous treatment may have on the participant. If such a factor is an issue, a washout or adaptation period may be incorporated to minimize the effects of the previous treatment. However, a proper design is constructed so that each treatment is administered in a similar fashion.

Furthermore, in a crossover design, comparisons are made within-subjects, whereas in a parallel design they are conducted between-groups. Also, proper power analysis in randomized clinical trials can be conducted beforehand to determine the size of the sample groups, but an ideal sample size may not always be feasible due to the ethical implications and the placebo exposure that may dismay potential participants in enrolling in the trial. In addition, due to the theoretical comparability of the two groups in randomized clinical trials, such designs possess strong internal validity but the ability to generalize or the strength of external validity in such designs is severely limited if the trial was based on a very homogenous group.

If proper randomization is not properly conducted in a randomized clinical trial, such a trial is considered quasi-randomized. In such a trial, the generation of allocating the subjects could entail bias. For example, quasi-randomization may be present if the subjects are assigned based on their patient record, social security number, or odd or even days of the week.

In the event that randomization is not performed but control groups are present, the trial is regarded as a controlled clinical trial; however, such a study design lacks the strength of a properly conducted randomized clinical trial by possessing potential confounds that may affect the true effect size of the interventions being observed.

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