Clinical Trial Design

A clinical trial must follow a design that is chosen based on the goals stated in the research protocol.

Government agencies stipulate that an appropriate method for a clinical trial must be selected. Two of the main methods for conducting clinical trials are the uncontrolled clinical trial and the controlled clinical trial. Controlled clinical trials can be conducted in different ways.

Differences Between Uncontrolled and Controlled Clinical Trials

An uncontrolled clinical trial is one without a control group, meaning that all the participants receive the same treatment.

By contrast, a controlled clinical trial separates participants into comparison groups. One group (the control group) receives the standard treatment or placebo, while the other group (the experimental group) receives the study treatment.

Several groups may receive the study treatment, for example, if different doses are being tested, or if the study treatment is given alone to one group, and in combination with another treatment to another group.

Controlled Clinical Trial Designs

Different controlled clinical trial methods determine:

If participants and the research team know who is receiving the treatment or the placebo or not (open-label trial, single-blind or double-blind trial).
If the distribution of participants in the clinical trial is random or not (randomized or non-randomized trial).
If each group of participants receives one treatment or several successive treatments (crossover trial or parallel group trial).

Open-label, single-blind and double-blind controlled trials

Open-label controlled clinical trial

The clinical trial investigator, the research team and the project participant groups know which treatment is being administered (placebo, standard treatment or study treatment).

Single-blind controlled clinical trial

The clinical trial investigator and the research team know which participants are in the experimental group (receiving the treatment) and which are in the control group (receiving the placebo), but the participants do not know. In some cases, it may be the study participants who are aware of their group assignment, while the study physician and research team are not.

Double-blind controlled clinical trial

Neither the clinical trial investigator nor the research team nor the project participants know which treatment is being given (placebo, standard treatment or study treatment).

The single-blind and double-blind methods prevent research team members and/or participants from affecting trial results by accident because of their expectations or bias concerning the treatment.

Randomized and non-randomized clinical trials

When participants are assigned at random to the different groups in a controlled clinical trial, usually using random selection software, we refer to the study as a randomized controlled clinical trial.

Random assignment of participants to any of the groups makes it less likely that individual behaviours or factors will affect the results of the trial. It also increases the likelihood of groups being comparable at the start of the trial and helps to conclude that any difference observed between groups at the end of the trial is due to the treatment.
When participants are assigned to the different groups in a controlled clinical trial using a non-random method, we refer to the study as a non-randomized controlled clinical trial. Assignment to different groups may be decided by the clinical trial investigator or by the research team.

Crossover or parallel-controlled clinical trials

Controlled clinical trials, whether randomized or non-randomized, open, single-blind or double-blind, can be conducted using either the crossover or parallel method.

Crossover controlled clinical trial

Project participants receive the standard treatment (or placebo) followed by the study treatment or vice versa (randomized order). No doses are given during the period between the two treatments. This action ensures that there are no possible lasting effects from the first treatment.

Parallel-controlled clinical trial

All participants in a group receive the same treatment (placebo, standard treatment or study treatment) from the start to the end of the trial.

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