The Pharmaceutical Journal
Vol 268 No 7188 p311-320
9 March 2002

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The Lancet (www.thelancet.com)

Risk of side effects overestimated with qualitative descriptions

Patients given qualitative rather than quantitative descriptions of side effects overestimate their risk, researchers from the universities of Reading and Leeds say. They asked 750 people to estimate the probability of having a side effect using qualitative and quantitative descriptions in four studies.

One study, involving 360 people, found that participants given the description "common" rated risk as 50 per cent compared with 9.5 per cent in those given the equivalent numerical description (2 per cent). For "rare" or the equivalent numerical value of 0.02 per cent, risk was rated as 21 per cent and 7 per cent, respectively.

The researchers criticise a European Union guideline recommending that frequency of side effects should be described using one of five terms ranging from very rare to very common. "If people are unable to estimate the risk of occurrence of side effects, they cannot be expected to make informed decisions about medicinal drug taking. Our results strongly suggest that the qualitative descriptions recommended by the EU lead to gross overestimation of risk," they conclude (Lancet 2002;359:853).