Clinical Study Terminology
A placebo-controlled study refers to a clinical study that compares an active product (e.g. dietary supplement, medication, etc.) to an inactive product (placebo). The placebo is usually prepared using the same ingredients as the active product, but without the active ingredient itself. This allows for a direct evaluation of the active substance in the clinical study as there are often “placebo” effects seen in a study. For example, in trials investigating products for pain relief associated with osteoarthritis, a placebo effect up to 30% is often seen in participants perception of pain relief over the course of the study, thus in order to say a product is effective, a reduction greater than 30% is necessary to overcome what is usually seen in participants on placebo.
Clinical studies may be referred to as single-blind, double-blind or triple-blind.
Single-blind studies are studies where the investigator (and investigator’s team) are blinded to the study products, but the participant knows what treatment he/she is taking. This usually occurs in studies where it is not possible to keep subjects blinded due to differences in products. For example, if one was studying the effects of dark chocolate, white chocolate may be used as a placebo. Obviously, subjects will know the difference. The clinic may appoint one staff member to dispense the products and calculate subject compliance. This staff member would not be involved in any other study procedures, ensuring the clinic staff remain blinded.
These are studies in which both the Investigator (and clinic staff) and participants are not aware of which product they are taking to prevent any potential bias associated with this knowledge. Double-blind and triple-blind are highly regarding to ensure that results are not influenced in any way.
Many “triple-blind” studies are actually called double-blind. Triple blind means that the investigator (and clinic staff), participants, and the statistician evaluating the data are all blinded to treatment. The blind is usually broken after all analysis is complete so as to prevent any bias by the statistician or influence of the data interpreter. Though the term “triple-blind” may not be used as commonly as double-blind, the statistician is often blinded until after all statistical analyses are complete during double-blind studies.
Randomization of study participants is done to provide balance between study groups with respect to baseline characteristics (age, gender, weight, etc.). Participants are randomized according to a randomization schedule provided to the investigator by the sponsor of the clinical study. Each subject will receive a unique randomization code based on the order they enter into the study. Each randomization code is associated with the product the participant is to receive. This maintains blinding of the study as the study product will be labeled with the unique randomization code rather than the identity of the product. The randomization schedule is created by an unblinded person who is independent of all study measures and assessments.
Many larger studies, especially pharmaceutical studies, are multi-centered. This means that there is more than one study site involved in the particular clinical trial. This is often done in order to recruit participants more quickly and to obtain a more general study population. Proper evaluation by the statistician will include tests to ensure data is similar between study sites to prevent this as a source of bias in the data set. Most phase III studies are multi-centered trials due to the large sample size, but some phase II studies may also be multi-centered.
Crossover studies are studies where all participants receive all treatments in an order. The order may be sequential (sequential crossover) or random (randomized crossover). In sequential studies, all participants will receive the treatments (or placebo) in the same sequence, as such these studies are open-label. In a randomized crossover trial, participants will be randomized to an order of treatments. The number of possible treatment orders is usually determined by the number of products to be investigated in the study.
Some trials will stratify participants based on one or more demographic characteristics. The characteristics are usually driven by the outcome to be measured in the study. For example, in osteoarthritis studies, body mass index (BMI) may be associated with osteoarthritis pain. In this case subjects would be stratified by BMI, ensuring that each BMI category is represented equally in each treatment group. Similarly, antioxidant status is influenced by smoking status, again in such studies, participants would be stratified by their smoking status (current, never, past). The investigator will receive a randomization schedule for each stratification to ensure that each characteristic is represented equally between treatment groups.
There are four recognized study phases in clinical research: Phase I, Phase II, Phase III and Phase IV. Phase I is usually “first in human” / pilot studies, but also includes bioavailability / pharmacokinetic studies. Sample sizes are usually small (10-80 subjects) and provide an indication of potential effectiveness. Phase II studies are usually run to determine the efficacy of the product. They may include 40-300 subjects. Phase III studies are usually run in a larger population (up to thousands of subjects) and are usually multi-centered. Phase IV studies are post-market surveillance studies, meaning information is gathered on the product after it is available on the market. Phase IV studies may provide further indications for the product, or add to the safety profile of the product.
A meta-analysis combines several studies, weighting each study based on sample size, quality and design and compares them statistically. They are often important in systematic reviews and are used to understand the effectiveness (efficacy) of a treatment or therapy.
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