Abstract -
Objective and Sample: This investigation assessed the comprehension of survival curves in a community sample of 88 young and middle-aged adults when several aspects of good practice for graphical communication were implemented, and compared comprehension for alternative presentation formats.
Design, Method and Measurements: After reading worked examples of using survival curves that provided explanation and answers, participants answered questions on survival data for pairs of treatments. Study 1 compared presenting survival curves for both treatments on the same figure against presentation via two separate figures. Study 2 compared presenting data for three possible outcome states via a single “multi-state” figure for each treatment against presenting each outcome on a separate figure (with both treatments on the same figure). Both studies compared alternative forms of questioning (e.g., “number alive” versus “number dead”). Numeracy levels (self-rated and objective measures) were also assessed.
Results: Comprehension was generally good – exceeding 90% correct answers on half of the questions – and was similar across alternative graphical formats. Lower accuracy was observed for questions requiring a calculation, but was only significantly lower when the requirement for calculation was not explicit (13-28% decrements in performance). In Study 1, this effect was most acute for those with lower levels of numeracy. Subjective (self-rated) and objective (measured) numeracy were both moderate positive predictors of overall task accuracy (r = .3).
Conclusions: A high degree of accuracy in extracting information from survival curves is possible, as long as any calculations that are required (e.g., finding differences between two survival rates) are made explicit. Therefore, practitioners need not avoid using survival curves in discussions with patients, though clear and explicit explanations are important.
Tim Rakow - Publications
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