Faculty of Health and Medical Sciences

Apply the evidence

Are the results clinically important?

Are the benefits clinically meaningful as well as statistically significant, and do the benefits outweigh any harms of the intervention or diagnostic test?

Click on each of the tabs below to explore aspects of clinical importance.

Results and benefits

  • What are the results and do you understand how they are presented?
    • The differences between relative (RRR) and absolute risk reductions (ARR) are often poorly understood by health professionals, and patients have even more trouble. However, you need to understand these concepts to communicate information to your patients. Read more about absolute and relative risk reduction.
    • Become familiar with concepts such as Kaplan Meier survival curves for trials of therapy, Forest plots for meta-analysis, and Receiver Operating Curves (ROC) for diagnostic tests. Read more about these concepts in the Resources section.
    • The number needed to treat (NNT) is calculated as 1/ARR. It is the number of people that you would have to treat with treatment B in order to save one additional life. In the examples above, treatment B may give a NNT that varies from 10 to 40 depending on the expected event rate. NNT will differ in individual patients as their baseline risk differs.
  • Assess whether the treatment effect is clinically relevant.
  • Determine what level of uncertainty surrounds the results.
  • Consider how results are put into context in the discussion.
  • Risks and toxicities

  • Ask yourself if the risks or toxicities outweigh the benefits of treatment.
    • What is the Number Needed to Harm (NNH)?
  • Clinical v statistical significance

    • Almost any difference can be statistically significant if a large enough clinical trial is done. However, a statistically significant clinical trial result does not always imply a clinically important result.
    • A clinically important result must show a difference or benefit that is large enough to be worth the costs, toxicities and inconveniences involved.

    For example, in 2007 a phase III clinical trial in advanced pancreatic cancer reported a statistically significant (p=0.038) improvement in patient survival from adding a novel targeted therapy to standard chemotherapy. However, the treatment produced an increase in median survival from 5.9 months to 6.2 months at a cost of many thousands of dollars and increased toxicity. This statistically significant result was of debatable clinical significance (3 week improvement in survival) and high economic cost.

    Moore MJ, Goldstein D, Hamm J et al. Erlotinib Plus Gemcitabine Compared With Gemcitabine Alone in Patients With Advanced Pancreatic Cancer: A Phase III Trial of the National Cancer Institute of Canada Clinical Trials Group. J Clin Oncol (2007); 25:1960-1966