Evaluating a combined (frequency and percentage) risk expression to communicate information on medicine side effects to patients

Peter Knapp, Peter Gardner, Brian McMillan, David K. Raynor, Elizabeth Wool

Research output: Contribution to journalArticlepeer-review


Objectives The study evaluated the interpretation of, and preferences for, numerical information on side-effect incidence when presented in three different formats. Methods It used a controlled design, with participants allocated at random to receive one of the three formats. Participants were recruited via a pop-up window on the CancerHelp UK website. The sample comprised 129 website users, of whom 96% were women and 86% had cancer, who received frequency information on four side effects of tamoxifen, using one of three risk expressions (percentages, e.g. ‘affects 25% of people’; frequencies, e.g. ‘affects 1 in 4 people’; combined, e.g. ‘affects 1 in 4 people (25%)’). They then interpreted information on tamoxifen and its effect on health, and estimates of side-effect frequency, and then stated a preference from the three risk expression formats. Key findings The results showed that the three formats did not influence participants’ ratings of the information or their side-effect estimates. However, more than half (53%) the participants preferred the combined (frequency and percentage) format. In conclusion, a combined risk expression format performed no worse than percentages or frequencies alone and was preferred by a majority. Conclusions The three risk expression formats did not differ in their effect on participants’ interpretations. However, the preferred format was the combined (frequency and percentage) risk expression.
Original languageEnglish
Pages (from-to)226-232
Number of pages7
JournalThe International journal of pharmacy practice
Issue number4
Publication statusPublished - Aug 2013

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