The impact of numeracy on verbatim knowledge of the longitudinal risk for prostate cancer recurrence following radiation therapy - Abstract

OBJECTIVE: Given the long natural history of prostate cancer, we assessed differing graphical formats for imparting knowledge about the longitudinal risks of prostate cancer recurrence with or without 'hormone' or 'androgen deprivation' therapy.

METHODS: Male volunteers without a history of prostate cancer were randomized to 1 of 8 risk communication instruments that depicted the likelihood of prostate cancer returning or spreading over 1, 2, and 3 years. The tools differed in format (line, pie, bar, or pictograph) and whether the graph also included no numbers, 1 number (indicating the number of affected individuals), or 2 numbers (indicting both the number affected and the number unaffected). The main outcome variables evaluated were graphical preference and knowledge.

RESULTS: A total of 420 men were recruited; respondents were least familiar and experienced with pictographs (P < 0.0001), and only 10% preferred this particular format. Overall accuracy ranged from 79% to 92%, and when assessed across all graphical subtypes, the addition of numerical information did not improve verbatim knowledge (P = 0.1). Self-reported numeracy was a strong predictor of accuracy of responses (odds ratio [OR] = 2.6, P = 0.008), and the impact of high numeracy varied across graphical type, having a greater impact on line (OR = 5.1; 95% confidence interval [CI] = 1.6-16; P = 0.04) and pie charts (OR = 7.1; 95% CI = 2.6-19; P =0.01), without an impact on pictographs (OR = 0.4; 95% CI = 0.1-1.7; P = 0.17) or bar charts (OR = 0.5; 95% CI = 0.1-1.8; P = 0.24).

CONCLUSION: For longitudinal presentation of risk, baseline numeracy was strongly prognostic for outcome. However, the addition of numbers to risk graphs improved only the delivery of verbatim knowledge for subjects with lower numeracy. Although subjects reported the least familiarity with pictographs, they were one of the most effective means of transferring information regardless of numeracy.

Written by:
Hamstra DA, Johnson SB, Daignault S2 Zikmund-Fisher BJ, Taylor JM, Larkin K, Wood A, Fagerlin A.   Are you the author?
Department of Radiation Oncology, University of Michigan, Ann Arbor Department of Health Behavior & Health Education, University of Michigan; Ann Arbor Department of Internal Medicine, University of Michigan, Ann Arbor Center for Bioethics and Social Sciences in Medicine, University of Michigan, Ann Arbor; VA Ann Arbor Center for Clinical Management Research, Ann Arbor, Michigan; Department of Psychology, University of Michigan, Ann Arbor; Department of Biostatistics, University of Michigan, Ann Arbor.  

Reference: Med Decis Making. 2014 Oct 2. pii: 0272989X14551639.
doi: 10.1177/0272989X14551639

PubMed Abstract
PMID: 25277673 Prostate Cancer Section