Study Design

Study design is a crucial determinant of the strength, validity, and subsequent usefulness of clinical research results. Study design is the methodology used to conduct the clinical research. Many different types of clinical research studies exist. The strength of the data depends upon the conditions used during the conduct of the trial. Also, these conditions help to eliminate bias by the investigator, patient, or others who are involved in the collection and analysis of the data. The most important conditions are blinding, randomization, and controlling. The randomized, controlled, double blind study is considered to be the clinical research ideal.

Blinding refers to the process in which the patient does not know whether he or she is receiving the test treatment or a placebo treatment. In the single blind design, the patient does not know which treatment he or she is receiving. The investigator knows, however, and this may lead to bias. Ideally, studies should be double blind, a condition in which neither the patient nor any of the other people who are actively involved in the study have knowledge of the treatment.

Randomization refers to the process in which the patients are randomly assigned to the various treatments. This insures that the test treatment and controls are allocated to the patient by chance, and not the choice of the investigator. Randomization eliminates the possibility that an investigator could sway study results.

Clinical research studies can be either controlled or uncontrolled. Controls can be either the standard treatment for the target disease (active controlled ) or a placebo (vehicle controlled). Many diseases have a natural tendency to wax and wane so study results can be misleading without a control group to serve as a comparator to the treatment group. Because controlled studies are a more reliable indicator of a treatment's effectiveness, uncontrolled studies are considered as preliminary or suggestive, or they may be disregarded altogether.

Another important component of study design is the determination of the sample size, or number of patients to include in the study. A sample size that is too small will yield a study in which the results are not strong enough (not statistically significant) to prove that the test treatment is effective. The sample size is based upon, among other things, the number of treatment and control groups in the study and an estimation of the expected differences between these groups.

The study design is contained within the study protocol, which is a detailed document that outlines every aspect of the study. The protocol is essentially a set of rules that the investigator(s) must follow. It covers such things as who may be entered into the study, how to collect and record data, and how to record and report adverse reactions. Violation of any of the rules set forth in the protocol can disqualify an investigator, a patient, or even the entire study.

Although the randomized, controlled, single and double blind studies are very common designs, there are other study designs which may be used. The sponsor may initially conduct dose-finding studies in order to find the optimal dose of a test drug to treat the target disease. In the cross-over design, patients receive both treatments being compared (or treatment and a placebo) which factors out inter-individual variability. Each patient would receive one treatment for a designated time period, their disease state would be evaluated, and then they would switch to the other treatment for a designated time period. Other, more complex study designs are also employed. However, with increasing complexity comes increasing difficulties in data analysis, interpretation, and validity.

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