Risk Estimates From an Online Risk Calculator Are More Believable and Recalled Better When Expressed as Integers

Abstract

BackgroundOnline risk calculators offer different levels of precision in their risk estimates. People interpret numbers in varying ways depending on how they are presented, and we do not know how the number of decimal places displayed might influence perceptions of risk estimates.ObjectiveThe objective of our study was to determine whether precision (ie, number of decimals) in risk estimates offered by an online risk calculator influences users’ ratings of (1) how believable the estimate is, (2) risk magnitude (ie, how large or small the risk feels to them), and (3) how well they can recall the risk estimate after a brief delay.MethodsWe developed two mock risk calculator websites that offered hypothetical percentage estimates of participants’ lifetime risk of kidney cancer. Participants were randomly assigned to a condition where the risk estimate value rose with increasing precision (2, 2.1, 2.13, 2.133) or the risk estimate value fell with increasing precision (2, 1.9, 1.87, 1.867). Within each group, participants were randomly assigned one of the four numbers as their first risk estimate, and later received one of the remaining three as a comparison.ResultsParticipants who completed the experiment (N = 3422) were a demographically diverse online sample, approximately representative of the US adult population on age, gender, and race. Participants whose risk estimates had no decimal places gave the highest ratings of believability (F 3,3384 = 2.94, P = .03) and the lowest ratings of risk magnitude (F 3,3384 = 4.70, P = .003). Compared to estimates with decimal places, integer estimates were judged as highly believable by 7%–10% more participants (χ2 3 =17.8, P < .001). When comparing two risk estimates with different levels of precision, large majorities of participants reported that the numbers seemed equivalent across all measures. Both exact and approximate recall were highest for estimates with zero decimals. Odds ratios (OR) for correct approximate recall (defined as being within 50% of the original estimate) were, for one decimal place, OR = 0.65 (95% CI 0.49–0.86), for two decimal places, OR = 0.70 (95% CI 0.53–0.94), and for three decimal places, 0.61 (95% CI 0.45–0.81). Exact recall showed a similar pattern, with larger effects.ConclusionsThere are subtle but measurable differences in how people interpret risk estimates of varying precision. Adding decimal places in risk calculators offers little to no benefit and some cost. Rounding to the nearest integer is likely preferable for communicating risk estimates via risk calculators so that they might be remembered correctly and judged as believable.

Blocks, Ovals, or People? Icon Type Affects Risk Perceptions and Recall of Pictographs

“…This is a robust model that estimates an individual’s risk of cardiovascular disease (CVD) within the next ten years based on her or his age, blood pressure, cholesterol or body mass index (BMI), and whether or not s/he smokes, is diabetic, and takes blood pressure medication. The model generates 10-year risk estimates that range from 1% to “more than 30%”, and all estimates were rounded to the nearest whole percentage based on recent research showing that integer risk statistics are perceived as more trustworthy than statistics with decimals [34]. Because the model applies only to people who have not already experienced CVD [33], we excluded any respondents who reported prior heart disease or stroke.…”

Decision Support for Patients

“…However, some work is underway in this area. Researchers at the University of Michigan are using human factors engineering principles to develop criteria for evaluating the usability of specific interactive VC/PE techniques (Witterman, Zikmund-Fisher, Waters, Gavaruzzi, & Fagerlin, 2011). Crump and Wedley (2011) are drawing from the fields of cognition and decision modeling to develop a framework for assessing the process aspects of interactive VC/PE.…”

A Psychological Perspective on Factors Predicting Prophylactic Salpingo‐Oophorectomy in a Sample of Italian Women from the General Population. Results from a Hypothetical Study in the Context of BRCA Mutations

“…These figures were based on estimates recently reported(Mavaddat et al 2013) rounded to the closest tens. This choice was based on previous work suggesting that: absolute risk reduction information should be provided (e.g.,Akl et al 2011), integers are better remembered and more believable than numbers with decimals(Witteman et al 2011), and patients better comprehend information with less details, that reduce the cognitive burden of comparing information(Peters et al 2007). …”