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Be cautious about using verbal descriptors of risk (rare, common). If used, ensure they are accompanied by statistical information

HL_man_bedDifferent people interpret terms such as rare, unusual and common in different ways, and numerical data should be used alongside these.

Evidence has shown that patients have a more accurate perception of risk if the probability of an event occurring is presented as numbers (e.g. 1 in 100) rather than in words (such as “rare”, “common”).

Why is this important?

These findings...add weight to the growing body of research highlighting the deficiencies in using verbal descriptors for conveying side effect risk, and the strength of using absolute frequency descriptors.

Knapp, Peter; Raynor, David K.; Woolf, Elizabeth; Gardner, Peter H.; Carrigan, Neil; McMillan, Brian., Communicating the Risk of Side Effects to Patients: An Evaluation of UK Regulatory Recommendations. (2009.) Vol. 32, No. 10, 2009, p. 837-849.. DRUG SAFETY.

This is the first evaluation of the full range of combined verbal and numerical risk expressions recommended in EMA guidance; it demonstrates that they can lead to significant risk overestimations when compared to numerical frequency bands alone. 

Knapp P, Gardener H, Woolf E., Combined verbal and numerical expressions increase perceived risk of medicine side-effects: a randomized controlled trial of EMA recommendations. (2015.) doi: 10.1111/hex.12344.. Health Expectations.

The use of verbal descriptors to improve the level of information about side effect risk leads to overestimation of the level of harm and may lead patients to make inappropriate decisions about whether or not they take the medicine.

Knapp P, Raynor D & Berry D., Comparison of two methods of presenting risk information to patients about the side effects of medicines. (2004.) 13:176-180.. Quality and Safety in Health Care.
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Resources to support you

  • Communicating Risk: introduction

    Risks and statistics are an essential part of patient information. This introductory factsheet discusses issues to consider as information professionals when thinking about communicating risk.

  • Risks and Probability

    A short guide to using numbers and percentages to express risk, with an example of making risks relevant.

  • Presenting information on risk

    General principles on how best to communicate risk.

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How have others done this?

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