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Evidence type

Randomised trials

Randomised trials are a key method for testing the effects of medical and health interventions. By randomly assigning participants, these studies aim to balance differences between groups and reduce bias, making their findings more reliable. However, they are not free from limitations, and careful interpretation is still needed.

Randomised trials—sometimes called randomised controlled trials (RCTs)—are regarded as a strong type of scientific evidence when testing the effects of medicines, interventions, or treatments. This is because randomisation aims to distribute known and unknown factors (confounders) evenly between the intervention group and comparison group.

What makes randomised trials stronger than other study types?

  • Randomisation: Participants are assigned to groups by chance, not by choice, which helps make the groups as similar as possible before the intervention starts.
  • Reduces bias: Random assignment cuts down on selection bias and some types of confounding.
  • Control groups: Many randomised trials include a placebo or standard-treatment control group for comparison.

Important factors and limitations

  • Sample size: Small trials can produce unreliable or inconclusive results, simply by chance.
  • Blinding: If participants and researchers do not know which group participants are in (blinding), this can further reduce bias. Unblinded trials are more vulnerable to bias.
  • Endpoints: Trials sometimes rely on "surrogate" endpoints (such as lab numbers) rather than direct measures like deaths or improved quality of life. Surrogate outcomes may not always predict meaningful benefits.
  • Duration and follow-up: Short studies may miss long-term effects or harms.
  • Generalisability: Results from one group or setting may not apply to other populations or real-world situations.
  • Reporting and publication bias: Positive or dramatic findings are more likely to be published, while negative or small effects may not be reported.

How to read randomised trial results

  • Check if the randomisation procedure and blinding are described clearly.
  • Look at the size and characteristics of the sample.
  • Consider whether the outcome measured is directly relevant to real-life health (not just a surrogate).
  • Find out if the trial ran long enough to detect both benefits and possible harms.
  • Be cautious of trial results that are not supported by larger or later studies.

In summary, randomised trials offer fewer opportunities for bias than many other study types, but they are not foolproof. Many randomised trials, especially small or short-term ones, may later be contradicted by larger or longer studies. It's always important to read beyond the headline and look at the whole trial report and its context within the wider body of evidence.

Reports

Related deHype reports

Specific public claims connected to this topic.

Report · Grade C Evidence check: Cancer jab can eradicate entire tumours in patients, trial shows The article reports on early results from an international clinical trial (OrigAMI-4), presented at the ASCO conference, testing the drug amivantamab in 102 patients with head and neck cancers that are resistant to standard treatments. The trial found that tumours shrank or disappeared in about a third of patients, with complete eradication in 15 cases. The jab is a targeted therapy that blocks EGFR and MET and activates immune response. Most side effects were mild to moderate, and ongoing evaluation is being conducted in additional cancer types. Report · Grade C Evidence check: Can fasting fight gum disease? Scientists find surprising link A small randomised controlled pilot study suggests short-term fasting-style cycles may reduce markers of gum inflammation, but the findings are preliminary, based on 28 participants and surrogate laboratory outcomes rather than direct clinical endpoints. Report · Grade B Evidence check: Scientists finally crack an “undruggable” pancreatic cancer target and nearly double survival The article claims that a new targeted therapy—daraxonrasib—for metastatic pancreatic cancer patients with KRAS mutations almost doubles overall survival compared to chemotherapy, based on a phase 3 trial of 500 patients, with secondary claims that this represents a paradigm shift, offering improved quality of life and milder side-effects versus standard care. Report · Grade C Evidence check: New ovarian cancer drug gives women more time and better quality of life - BBC News The article reports that mirvetuximab soravtansine, now available on the NHS, extends average survival in patients with specific hard-to-treat ovarian cancers from 12.8 to 16.5 months, with improved quality of life and fewer side effects than conventional chemotherapy. It is only suitable for cancers with the folate receptor alpha marker, reportedly benefiting about 30-40% of those whose cancers are resistant to standard chemotherapy. Patient and clinician testimonials support these claims, but no direct link to the clinical trial publication is given in the article. Report · Grade C Evidence check: A personalized vaccine for melanoma cut the risk of cancer returning after five years The NBC News article covers new results from a clinical trial on an experimental personalised mRNA vaccine for melanoma, developed by Moderna and Merck, suggesting reduced risk of cancer returning over five years. However, the article does not provide full trial details, peer-reviewed publication, or data on longer-term safety and generalizability.

Helpful evidence guides

How deHype grades claims Learn how deHype evaluates health and science claims with a transparent grading system based on strength, relevance, and quality of evidence. How to read a health headline A practical guide to spotting overstatement and understanding the evidence behind health and science headlines.

Related evidence pages

Animal studies Animal studies can provide valuable insights into biological processes and potential effects of interventions. However, results from animal experiments may not translate to humans. This page explains why animal research can inform but not confirm health claims about people. Cell studies How in-vitro and cell-line findings should be interpreted in health headlines. Cell studies investigate the effects of substances or genetic changes in isolated cells outside the human body. While these studies can show how something may work at a basic biological level, their results do not directly apply to human health without further research. Guidelines Guidelines translate research evidence into recommendations for clinical practice, but their strength can vary depending on the available evidence, expert interpretation, and other practical factors. Observational studies Observational studies look for associations in real-world populations but do not automatically prove that one factor causes another. Other explanations—including confounding and reverse causation—are important to consider when interpreting their results. Systematic reviews Systematic reviews summarise multiple studies using transparent, pre-specified methods. Their strength as evidence depends not only on their process but also on the quality and relevance of the included studies.
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