"Order effect" in the provision of medication information

To the Editor: One concern that medical practitioners and pharmacists have about patient counselling is the uncertainty about the amount of information which should be given to patients, especially regarding possible adverse reactions to medications.1 Studies have found that providing information on possible adverse reactions can affect patients' willingness to take the medication.1

Research in cognitive psychology provides clear evidence that the order in which information is presented has a significant influence on judgement. Information received first is likely to have a disproportionately large effect on judgement, the "primacy effect".2-4 Despite clear evidence supporting the "order effect" in diverse areas, research has not been undertaken to investigate whether the order effect is present in medication information.

To test the hypothesis that differently ordered sequences of the same information about a drug can result in different judgements,5 804 subjects were presented with a short description of a fictitious medication. The descriptions were presented in one of two formats (Box): (A) positive–negative (therapeutic benefits followed by potential adverse reactions) or (B) negative–positive order (potential adverse reactions followed by therapeutic benefits). The surveys were randomly distributed to university students, mindful of the limitation of extrapolating the data to the general population. Subjects rated the medication (from very bad to very good) and the likelihood of taking the medication (from very unlikely to very likely) on seven-point Likert scales. For analysis, we used the independent sample t test, which is robust and therefore considered suitable for this analysis.