Older people's understanding of cumulative risks when provided with annual stroke risk information.

Understanding how cumulative health risks increase over time constitutes an important part of decision making about treatment risks and benefits. In this study, wide ranging perceptions of cumulative risk led to significant overestimation and underestimation of risks over time. Time has shown to significantly impact on the personal interpretation of cumulative risk information by patients, with many subjects struggling to understand the concept of cumulative risks. This suggests that a careful explanation of the effect of cumulative risk over time to patients should contribute to more effective decision making.