Category Archives: Medical Decision Making

Health Numeracy

numeracyimagesIsaac Lipkus  and Ellen Peters authored: “Understanding the Role of Numeracy in Health: Proposed Theoretical Framework and Practical Insights,”  It was published in Health Education Behavior in December 2009.  I find it to be a very useful article.  There are articles summarizing all the research in the area, and articles explaining the best way to measure numeracy, and many books and articles showing the many human weaknesses with respect to numeracy.  This article does a good job of putting the pieces together.

Numeracy, that is how facile people are with mathematical concepts and their applications.  Lipkus and Peters propose six critical  functions of health numeracy. These functions are integrated into a theoretical framework on health numeracy that has implications for risk-communication and medical-decision-making processes. They examine practical underpinnings for targeted interventions aimed at improving such processes as a function of health numeracy.

I. Numeracy facilitates computation.

Men and women ages 50 to 80 were presented with information about treatment efficacy in one of four formats:  numbers needed to treat, absolute risk reduction, relative risk reduction, or a combination of the three formats. Those with poorer numeracy were less likely to identify the most effective treatment and were less able to accurately compute degree of benefit.
II. Numeracy encourages more information seeking and greater depth of processing.

Recent research has shown that the highly numerate integrate the perceived attractiveness of risky and riskless options in traditional framing choices more than the less numerate; the less numerate respond more superficially instead to the frame of the information provided. Consistent with dual process models of attitude change, greater seeking and scrutiny of numerical data can increase its persuasiveness and hence its effects on decisions/behaviors, should the data be judged credible, accurate, and deemed personally relevant.

III. Numeracy improves interpretation of the meaning of provided numbers.

In general, the less numerate provide subjective risk estimates that exceed those provided by an “objective” criterion. In choice decisions, the less numerate are more likely to select options that do not maximize expected utility. Whereas the highly numerate appear to derive affective meaning from the given numbers and make decisions from this meaning, the less numerate rely less on specified probabilities and other sources of numeric information

IV. Numeracy facilitates assessments of likelihood and value

Numeracy is related to the consistency with which individuals provide mathematically equivalent numerical responses on different risk perception scales.  Those who were more numerate were more likely to provide identical (i.e., mathematically equivalent) answers on multiple scales.

V. Numeracy can increase or decrease acceptance of numerical data

Consistent with the less numerate trusting numeric data less, Peters and colleagues found that the less numerate also appeared to use it less and be influenced more by competing, less relevant affective considerations; the highly numerate drew more precise affective meaning from numbers and numerical comparisons that appeared to guide their decisions instead. In one study, subjects were offered a prize if they drew a colored jellybean from their choice of one of two bowls. The first Bowl A contained 9 colored and 91 white beans; Bowl B contained 1 colored and 9 white beans, so the odds of success were objectively better in Bowl B. Nevertheless, participants low in numeracy often chose Bowl A (33% and 5% of low and high numerate, respectively, chose from Bowl A) because “it looked more inviting.” Participants were asked about their feelings to the 9% chance of winning in Bowl A on a scale ranging from very bad to very good; they were also asked to report how clear those feelings were. Compared to the less numerate, high-numerate participants reported feelings towards the objectively lower 9% chance that were more clear and negative compared to the less numerate. This secondary affect (likely produced through a comparison of the objective probabilities in the two bowls) appeared to drive choices of the highly numerate.

VI. Numeracy promotes behavior change

This function suggests that numeracy may affect the motivation to take action and engage in behaviors based on quantitative information. Numeracy may either increase or decrease the likelihood of action perhaps through one or more of the functional values discussed (e.g., information seeking, computation, interpretation of meaning, etc.).


Atrial Fibrillation

afindexDr Thomas Tape wrote an article “Coherence and correspondence in medicine” that appeared in the March 2009 edition of Judgment and Decision Making.  As you might expect, Dr Tape is applying some of the ideas of Kenneth Hammond to medicine.  Tape notes that the distinction between coherence (making logical sense) and correspondence (being empirically correct) seldom appears in the medical literature.

Tape suggests that the field of medicine began with coherence approaches and has only recently adopted correspondence approaches at all. The original rationale for bloodletting was based on the idea that disease comes from an imbalance of humors.  This coherent argument was around for hundreds of years before being dispelled.  It seems surprising that patient outcome was not the indicator of choice, but even today with medical progress and sophisticated statistics, it is not so easy to tell what works.

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