title: Communicating data about the benefits and harms of treatment: a randomized trial.
abstract: BACKGROUND
  Despite limited evidence, it is often asserted that natural frequencies (for example, 2 in 1000) are the best way to communicate absolute risks.
  
  
  OBJECTIVE
  To compare comprehension of treatment benefit and harm when absolute risks are presented as natural frequencies, percents, or both.
  
  
  METHODS
  Parallel-group randomized trial with central allocation and masking of investigators to group assignment, conducted through an Internet survey in September 2009. (ClinicalTrials.gov registration number: NCT00950014)
  
  
  METHODS
  National sample of U.S. adults randomly selected from a professional survey firm's research panel of about 30,000 households.
  
  
  METHODS
  2944 adults aged 18 years or older (all with complete follow-up).
  
  
  METHODS
  Tables presenting absolute risks in 1 of 5 numeric formats: natural frequency (x in 1000), variable frequency (x in 100, x in 1000, or x in 10,000, as needed to keep the numerator >1), percent, percent plus natural frequency, or percent plus variable frequency.
  
  
  METHODS
  Comprehension as assessed by 18 questions (primary outcome) and judgment of treatment benefit and harm.
  
  
  RESULTS
  The average number of comprehension questions answered correctly was lowest in the variable frequency group and highest in the percent group (13.1 vs. 13.8; difference, 0.7 [95% CI, 0.3 to 1.1]). The proportion of participants who "passed" the comprehension test (≥13 correct answers) was lowest in the natural and variable frequency groups and highest in the percent group (68% vs. 73%; difference, 5 percentage points [CI, 0 to 10 percentage points]). The largest format effect was seen for the 2 questions about absolute differences: the proportion correct in the natural frequency versus percent groups was 43% versus 72% (P < 0.001) and 73% versus 87% (P < 0.001).
  
  
  CONCLUSIONS
  Even when data were presented in the percent format, one third of participants failed the comprehension test.
  
  
  CONCLUSIONS
  Natural frequencies are not the best format for communicating the absolute benefits and harms of treatment. The more succinct percent format resulted in better comprehension: Comprehension was slightly better overall and notably better for absolute differences.
  
  
  BACKGROUND
  Attorney General Consumer and Prescriber Education grant program, the Robert Wood Johnson Pioneer Program, and the National Cancer Institute.
authors.affiliation: Veterans Affairs Outcomes Group, White River Junction, Vermont 05009, USA.
authors.forename: Steven
authors.initials: S
authors.lastname: Woloshin
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Schwartz
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003142:Communication; D032882:Comprehension; D064420:Drug-Related Side Effects and Adverse Reactions; D004522:Educational Status; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010353:Patient Education as Topic; D018570:Risk Assessment; D016896:Treatment Outcome; D055815:Young Adult