Nathan F. Dieckmann

How Numeracy Influences Risk Comprehension and Medical Decision Making

We review the growing literature on health numeracy, the ability to understand and use numerical information, and its relation to cognition, health behaviors, and medical outcomes. Despite the surfeit of health information from commercial and noncommercial sources, national and international surveys show that many people lack basic numerical skills that are essential to maintain their health and make informed medical decisions. Low numeracy distorts perceptions of risks and benefits of screening, reduces medication compliance, impedes access to treatments, impairs risk communication (limiting prevention efforts among the most vulnerable), and, based on the scant research conducted on outcomes, appears to adversely affect medical outcomes. Low numeracy is also associated with greater susceptibility to extraneous factors (i.e., factors that do not change the objective numerical information). That is, low numeracy increases susceptibility to effects of mood or how information is presented (e.g., as frequencies vs. percentages) and to biases in judgment and decision making (e.g., framing and ratio bias effects). Much of this research is not grounded in empirically supported theories of numeracy or mathematical cognition, which are crucial for designing evidence-based policies and interventions that are effective in reducing risk and improving medical decision making. To address this gap, we outline four theoretical approaches (psychophysical, computational, standard dual-process, and fuzzy trace theory), review their implications for numeracy, and point to avenues for future research.

Less Is More in Presenting Quality Information to Consumers

Much effort has been put into improving measures of health care quality. Although early research suggested that consumers made little use of quality reports, most reports were based on nonstandardized measures and were not user friendly. Information presentation approaches, however, will have a significant influence on what information is attended and used. The present research examines whether information presentation methods differentially influence consumers who differ in numeric skills. Results of three studies support the idea that “less is more” when presenting consumers with comparative performance information to make hospital choices. Results were particularly strong for those lower in numeracy, who had higher comprehension and made better choices when the information-presentation format was designed to ease the cognitive burden and highlight the meaning of important information. These findings have important implications for the sponsors of comparative quality reports designed to inform consumer decision making in health care.

Bringing Meaning to Numbers: The Impact of Evaluative Categories on Decisions.

Decision makers are often quite poor at using numeric information in decisions. The results of 4 experiments demonstrate that a manipulation of evaluative meaning (i.e., the extent to which an attribute can be mapped onto a good/bad scale; this manipulation is accomplished through the addition of visual boundary lines and evaluative labels to a graphical format) has a robust influence in health judgments and choices and across diverse adult populations. The manipulation resulted in greater use of numeric quality-of-care information in judgments and less reliance on an irrelevant affective state among the less numerate. Recall results for provided quality-of-care numbers suggested that the manipulation did not influence depth of number processing with the exception of cost information that was not remembered as well. Results of a reaction-time paradigm revealed that feelings were more accessible than thoughts in the presence of the manipulation, suggesting that the effect may be due, at least in part, to an affective mechanism. Numeric information is often provided in decisions, but may not be usable by consumers without assistance from information providers. Implications for consumer decision making and the functions of affect are discussed.

The use of narrative evidence and explicit likelihood by decisionmakers varying in numeracy.

Decisionmakers are often presented with explicit likelihood assessments (e.g., there is a 10% chance that an attack will occur over the next three months) and supporting narrative evidence in forecasting and risk communication domains. Decisionmakers are thought to rely on both numerical and narrative information to the extent that they perceive the information to be diagnostic, accurate, and trustworthy. In two studies, we explored how lay decisionmakers varying in numeracy evaluated and used likelihood assessments and narrative evidence in forecasts. Overall, the less numerate reported higher risk and likelihood perceptions. In simple probabilistic forecasts without narrative evidence, decisionmakers at all levels of numeracy were able to use the stated likelihood information, although risk perceptions of the less numerate were more affected by likelihood format. When a forecast includes narrative evidence, decisionmakers were better able to use stated likelihood in a percentage as compared to frequency or verbal formats. The more numerate used stated likelihood more in their evaluations whereas the less numerate focused more on the narrative evidence. These results have important implications for risk analysts and forecasters who need to report the results of their analyses to decisionmakers. Decisionmakers varying in numerical ability may evaluate forecasts in different ways depending on the types of information they find easiest to evaluate.

Explaining the Effect of Education on Health A Field Study in Ghana

Higher education (or more years of formal schooling) is widely associated with better health, but the underlying causes of this association are unclear. In this study, we tested our schooling-decision-making model, which posits that formal education fosters intellectual ability, which in turn provides individuals with enduring competencies to support better health-related behaviors. Using data from a field study on formal education in 181 adults in rural Ghana, we examined health-protective behaviors related to HIV/AIDS infection, a critical health issue in Ghana. As expected, individuals with more education practiced more protective health behaviors. Our structural equation modeling analysis showed that cognitive abilities, numeracy, and decision-making abilities increased with exposure to schooling, and that these enhanced abilities (and not HIV/AIDS knowledge) mediated the effects of education on health-protective behavior. Research and policy implications for HIV prevention efforts in sub-Saharan Africa are discussed.

An Empirical Assessment of Meta-Analytic Practice

In the three decades after the publication of the first meta-analyses in the behavioral sciences, hundreds of articles and a number of technical guides have emerged concerning meta-analytic practice and reporting standards. The purpose of the present study is to review the practice and reporting standards of a random sample of published meta-analyses (n = 100) in psychology and related disciplines in the decade from 1994 through 2004. We focus on practice and reporting at each stage of the meta-analytic process and explore differences between psychological subdisciplines. These findings suggest that the practice of meta-analysis in the last decade has not yet converged on a set of common standards, though some expert recommendations are beginning to be heeded. Authors should be attentive to proper procedure and reporting in light of the numerous threats to the validity of a meta-analysis. Ironically, even though meta-analysts often struggle with incomplete or inconsistent reporting in primary research they are themselves not entirely consistent in reporting their methods and results.

Conflicting health information: a critical research need

Conflicting health information is increasing in amount and visibility, as evidenced most recently by the controversy surrounding the risks and benefits of childhood vaccinations. The mechanisms through which conflicting information affects individuals are poorly understood; thus, we are unprepared to help people process conflicting information when making important health decisions. In this viewpoint article, we describe this problem, summarize insights from the existing literature on the prevalence and effects of conflicting health information, and identify important knowledge gaps. We propose a working definition of conflicting health information and describe a conceptual typology to guide future research in this area. The typology classifies conflicting information according to four fundamental dimensions: the substantive issue under conflict, the number of conflicting sources (multiplicity), the degree of evidence heterogeneity and the degree of temporal inconsistency.