How Time-Trend Tasks Are Affected by Probability Format: A Making Numbers Meaningful Systematic Review

Background. To develop guidance on the effects of format on communication of health probabilities, the Making Numbers Meaningful team conducted a systematic review. Purpose. This article (one of a series) covers research on time-trend tasks, in which participants evaluate stimuli for information about probability trends, such as changing chances of cancer recurrence over time. Data Sources. MEDLINE, Embase, CINAHL, the Cochrane Library, PsycINFO, ERIC, ACM Digital Library; hand search of 4 journals. Study Selection. We conducted independent dual screening to identify experimental or quasi-experimental research comparing 2 or more formats for presenting quantitative health information to lay audiences. This article reports on 11 findings from 6 unique studies. Data Extraction. Independent dual extraction of information on stimulus (data in a data presentation format), task, and perceptual, affective, cognitive, and behavioral outcomes. Data Synthesis. We identified research on the impact of format on the following outcomes: contrast, computation, effectiveness perceptions, health behaviors and behavioral intentions, discrimination, and preference. Strong evidence suggests that graphing probability curves over longer (rather than shorter) time periods increases perceived differences between curves (effectiveness perception outcome). Weak evidence suggested 1) survival versus mortality curves do not affect perceived differences between curves or ability to perform computations, 2) survival curves may help people identify the option with the highest survival, and 3) graphing probabilities over longer time periods may not affect the ability to identify the highest survival. Limitations. Granular data extraction and evidence syntheses lead to narrow conclusions rather than broader statements. Conclusions. The very limited evidence available about probability time-trend tasks is primarily about the effects of framing (survival v. mortality curves) and the effects of using shorter versus longer time periods.

This systematic review found that few studies of probability trend data compared similar formats or used comparable outcome measures.The only strong piece of evidence was that graphing probabilities over longer time periods such that the distance between curves widens will tend to increase the perceived difference between the curves.Weak evidence suggests that survival curves (versus mortality curves) may make it easier to identify the option with the highest overall survival.Weak evidence suggests that graphing probabilities over longer (rather than shorter) time periods may increase the ability to distinguish between small survival differences.Evidence was insufficient to determine whether any format influenced behaviors or behavioral intentions.