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Tuesday, October 21, 2008
Columbus A-C (Hyatt Regency Penns Landing)
PURPOSE OF THE STUDY:
Base-rate statistics are available for a range of events in medicine, including cholesterol and heart disease. People’s tendency to neglect such information has received considerable attention in clinical decision-making literature. To our knowledge, however, no study has tested whether using icon arrays (i.e., graphical representations symbolizing affected individuals) to communicate medical risks could help people to take base-rates into account. This is the main purpose of our experiment.
METHOD:
A total of 116 participants were presented with four medical scenarios of the usefulness of hypothetical new drugs for reducing the risk of dying from a heart attack. Relative risk reduction in all scenarios was set at 40%. The overall number of patients who did and did not take the drugs was manipulated within subjects to be either 500/500, 500/100, 100/500, or 100/100, where the numerator and denominator of the ratio reflect the number of patients who did and did not take the drug, respectively. Independently of this manipulation, half of the participants received, in addition to the numerical information, two icon arrays presenting the risk of dying of heart attack when the drug was and was not taken. As dependent variables, accuracy of risk understanding and perception of risk reduction were measured.
RESULTS:
When only numeral information about medical risks was provided, participants ignored base rates: they overestimated (underestimated) risk reduction when the number of patients who did not take the drug was higher (lower) than the number of those who took the drug. Interestingly, when icon arrays were added to the numerical information, base-rate neglect disappeared (η²= .24). Participants’ perceptions of risk reduction were in line with these results (η²= .19).
CONCLUSIONS:
Icon arrays are helpful in communicating risk reductions because they increase accuracy of risk understanding and perception of risk reduction. We offer some guidelines about how base rates can be communicated in a way that is useful to individuals who need to make decisions about their health.
Base-rate statistics are available for a range of events in medicine, including cholesterol and heart disease. People’s tendency to neglect such information has received considerable attention in clinical decision-making literature. To our knowledge, however, no study has tested whether using icon arrays (i.e., graphical representations symbolizing affected individuals) to communicate medical risks could help people to take base-rates into account. This is the main purpose of our experiment.
METHOD:
A total of 116 participants were presented with four medical scenarios of the usefulness of hypothetical new drugs for reducing the risk of dying from a heart attack. Relative risk reduction in all scenarios was set at 40%. The overall number of patients who did and did not take the drugs was manipulated within subjects to be either 500/500, 500/100, 100/500, or 100/100, where the numerator and denominator of the ratio reflect the number of patients who did and did not take the drug, respectively. Independently of this manipulation, half of the participants received, in addition to the numerical information, two icon arrays presenting the risk of dying of heart attack when the drug was and was not taken. As dependent variables, accuracy of risk understanding and perception of risk reduction were measured.
RESULTS:
When only numeral information about medical risks was provided, participants ignored base rates: they overestimated (underestimated) risk reduction when the number of patients who did not take the drug was higher (lower) than the number of those who took the drug. Interestingly, when icon arrays were added to the numerical information, base-rate neglect disappeared (η²= .24). Participants’ perceptions of risk reduction were in line with these results (η²= .19).
CONCLUSIONS:
Icon arrays are helpful in communicating risk reductions because they increase accuracy of risk understanding and perception of risk reduction. We offer some guidelines about how base rates can be communicated in a way that is useful to individuals who need to make decisions about their health.
See more of: Poster Session III
See more of: 30th Annual Meeting of the Society for Medical Decision Making (October 19-22, 2008)