Berry, D. C., Knapp, P., & Raynor, T. (2006). Expressing medicine side effects: assessing the effectiveness of absolute risk, relative risk, and number needed to harm, and the provision of baseline risk information. Patient education and counseling, 63(1), 89-96.

Berry, D.; Knapp, P.; Raynor, T.

2006

Berry, D. C., Knapp, P., & Raynor, T. (2006). Expressing medicine side effects: assessing the effectiveness of absolute risk, relative risk, and number needed to harm, and the provision of baseline risk information. Patient education and counseling, 63(1), 89-96.

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To assess the effectiveness of absolute risk, relative risk, and number needed to harm formats for medicine side effects, with and without the provision of baseline risk information. A two factor, risk increase format (relative, absolute and NNH) baseline (present/absent) between participants design was used. A sample of 268 women was given a scenario about increase in side effect risk with third generation oral contraceptives, and were required to answer written questions to assess their understanding, satisfaction, and likelihood of continuing to take the drug. Provision of baseline information significantly improved risk estimates and increased satisfaction, although the estimates were still considerably higher than the actual risk. No differences between presentation formats were observed when baseline information was presented. Without baseline information, absolute risk led to the most accurate performance. The findings support the importance of informing people about baseline level of risk when describing risk increases. In contrast, they offer no support for using number needed to harm.

The results of this study provide strong empirical support for the inclusion of baseline information in risk communications involving comparisons between different levels of risk, and are in line with the predictions made at the outset. Informing people about the baseline level of risk of venous thrombosis improved risk estimates for both second and third generation preparations. Baseline information also led to enhanced ratings of satisfaction with the information provided and ease of judging risk. When people were informed about the baseline, there were no significant differences between the three different presentation formats on risk estimates. Provision of baseline information had no effect on ratings of likelihood of continuing to take the pill. Women given the absolute risk presentation format provided significantly higher ratings on this measure, irrespective of whether or not they were aware of the baseline.

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