Words alone

Be cautious when the size of effects is only described with words.

Describing the effect of a health action in words can be helpful, but the description should be considered together with a numerical description of the size of the effect. Words can be easier to understand than numbers, but they can mean different things to different people and can be used to trick people.


In a comparison, the effect of a health action is found by looking for differences in outcomes; it is a numerical concept. For example, 6 out of 10 people may be better after one week with a treatment and 5 out of 10 people may be better without that treatment. Then the effect of the treatment (the difference) is 1 more person out of 10 who will be better with the treatment. However, the numbers are not usually this easy; they may be hard to understand. Describing effects with words (qualitative descriptions) may be easier to understand. However, qualitative descriptions of effects may mean different things to different people. For example, saying that a treatment will ‘slightly reduce’, ‘reduce’, or ‘greatly reduce’ the chance of a harm; or that a side effect is ‘frequent’ or ‘rare’ mean different things to different people. In addition, descriptions of the effects of health actions may use manipulative language. For example, they may promise ‘amazing results’ or describe treatments as ‘natural’, implying that they are safe because of that.

People’s understanding of qualitative descriptions of effects can affect their decisions. Use of consistent language that has been user tested can improve the understanding, usability, and usefulness of information about the effects of health actions. Descriptions that use combinations of words, numbers and tables can help people to find and understand the effects of health actions.


A randomized trial compared words describing the effects of health actions (qualitative descriptions), such as “common” and “rare” to descriptions using numbers (quantitative descriptions). It found that those qualitative descriptions were associated with overestimation of the chance of harms. Patients shown qualitative descriptions had more negative impressions of the medicine than those shown quantitative descriptions, and they were more likely to say that the information would affect their decision to take the medicine.

Remember: When possible, consider the numbers that describe how big an effect of a health action is and not just the words. Descriptions using words can be misleading.

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