5.3 - Randomised Control Trials
What are randomised control trials?
Randomised control trials (RCTs) are a type of experimental method widely used in clinical and health psychology research. Often called the 'gold standard' for testing new treatments, they help researchers determine whether a drug, therapy, or intervention truly works.
RCTs increase the validity of findings by reducing influences from other factors. For example, they can distinguish real improvements caused by the treatment from those due to participants' expectations.
Key features of RCTs
- Random allocation - Participants are assigned to groups by chance.
- Experimental condition - The group that receives the actual treatment, drug, or intervention being tested.
- Control condition - The comparison group that does not receive the active treatment, often getting a placebo instead.
- Placebo - A fake treatment with no active ingredients, designed to look identical to the real one. This helps control for psychological effects.
By comparing outcomes between groups, researchers can attribute differences to the treatment itself rather than chance or other influences.
Blind designs in RCTs
To further improve validity, RCTs use blind designs. These prevent knowledge of group allocation from affecting behaviour or measurements.
Single-blind design
In a single-blind design, only the participants are unaware of whether they are receiving the real treatment or the placebo. This reduces the expectancy effect, where participants improve simply because they believe the treatment will work.
Double-blind design
A double-blind design takes this further by keeping both participants and researchers blind to group allocation. Researchers measuring symptoms or outcomes do not know who is in which group. This minimises experimenter bias, where a researcher's expectations might unconsciously influence how they record results.
How RCTs measure treatment effects
RCTs follow a structured process to assess whether a treatment is effective. This involves taking measurements at key points and accounting for natural improvements that might occur without the real treatment.
The process of conducting an RCT:
- Baseline measurement - Researchers assess participants' symptoms or conditions before any treatment begins.
- Treatment administration - Participants in the experimental group get the real intervention, while the control group receives the placebo.
- Post-treatment measurement - Symptoms are measured again after the treatment period.
- Analysis of results - Researchers compare changes between groups. Any greater improvement in the experimental group suggests the treatment's effectiveness.
Understanding the placebo effect
The placebo effect occurs when participants in the control group show improvement despite receiving no active treatment. This can happen due to psychological factors, such as hope or belief in the process. In an RCT, if the experimental group improves significantly more than the placebo group, the difference is attributed to the independent variable - the active ingredient or key element of the treatment.
Evaluating randomised control trials
Like all research methods in psychology, RCTs have both advantages and limitations.
Strengths and weaknesses of RCTs:
| Strengths | Weaknesses |
|---|---|
| High validity through objectivity - Blind designs reduce experimenter bias (where researchers' expectations affect results) and demand characteristics (where participants alter behaviour to meet perceived expectations). This leads to more reliable conclusions. | Ethical issues with informed consent - Although participants are informed about the randomization and blinding procedures beforehand, the complexity of these processes and participants' inability to know their specific group allocation raise concerns about the quality and completeness of informed consent. |
| Controlled testing of interventions - RCTs allow treatments and therapies to be examined in a systematic way, isolating cause-and-effect relationships. This is essential for evidence-based practice in clinical psychology. | Ethical concerns for control groups - Those in the placebo condition may be denied potentially beneficial treatments, which could harm their wellbeing, especially in studies of serious conditions. |