title: Expressing medicine side effects: assessing the effectiveness of absolute risk, relative risk, and number needed to harm, and the provision of baseline risk information.
abstract: OBJECTIVE
  To assess the effectiveness of absolute risk, relative risk, and number needed to harm formats for medicine side effects, with and without the provision of baseline risk information.
  
  
  METHODS
  A two factor, risk increase format (relative, absolute and NNH)xbaseline (present/absent) between participants design was used. A sample of 268 women was given a scenario about increase in side effect risk with third generation oral contraceptives, and were required to answer written questions to assess their understanding, satisfaction, and likelihood of continuing to take the drug.
  
  
  RESULTS
  Provision of baseline information significantly improved risk estimates and increased satisfaction, although the estimates were still considerably higher than the actual risk. No differences between presentation formats were observed when baseline information was presented. Without baseline information, absolute risk led to the most accurate performance.
  
  
  CONCLUSIONS
  The findings support the importance of informing people about baseline level of risk when describing risk increases. In contrast, they offer no support for using number needed to harm.
  
  
  CONCLUSIONS
  Health professionals should provide baseline risk information when presenting information about risk increases or decreases. More research is needed before numbers needed to harm (or treat) should be given to members of the general populations.
authors.affiliation: Pro-Vice-Chancellor's Office, University of Reading, Whiteknights House, Whiteknights, Reading RG6 6AH, UK. D.C.Berry@Reading.ac.uk
authors.forename: Dianne C
authors.initials: DC
authors.lastname: Berry
authors.forename: Peter
authors.initials: P
authors.lastname: Knapp
authors.forename: Theo
authors.initials: T
authors.lastname: Raynor
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D003276:Contraceptives, Oral / Q000009:adverse effects*; D003627:Data Interpretation, Statistical; D004739:England; D005163:Factor Analysis, Statistical; D005260:Female; D006801:Humans; D007258:Informed Consent; D008875:Middle Aged; D010174:Pamphlets; D010353:Patient Education as Topic / Q000379:methods*; D017060:Patient Satisfaction; D012306:Risk; D018570:Risk Assessment / Q000379:methods*; D012307:Risk Factors; D040242:Risk Reduction Behavior; D011795:Surveys and Questionnaires; D013664:Teaching Materials; D013923:Thromboembolism / Q000139:chemically induced / Q000453:epidemiology; D014930:Women / Q000193:education / Q000523:psychology
chemical_list: D003276:Contraceptives, Oral