Purpose: The effectiveness of interventions for chronic diseases can be expressed in terms of absolute risk reduction (ARR, NNT) or relative risk reduction (RRR), or life extension (LE). We aimed at: (i) exploring which single format yields decisions that are closest to those of the “fully” informed individual; (ii) explore which format is preferred by individuals. Methods: A random sample of 4,000 non-institutionalized individuals aged 40-59 were invited to a face-to-face interview and asked about preferences for a hypothetical preventive drug. In total, 1,491 (37%) interviews were completed. Respondents were randomized to 24 different interview formats of which 16 (n=1,169) are presented here. Here, respondents were randomly allocated to receive first one single piece of information (ARR, NNT, RRR or LE) and then indicate preferences for the drug on a 1-10 scale (1=definitely no; 10=definitely yes). Subsequently they were given “full information” (all four pieces + pictorial representation with crowd figures (PR)) and asked again to indicate preferences on the same scale. Finally, they were asked 3 questions to test numeracy. Results: On the 1-10 scale, the mean change in preference from primary to “full information” was +0.12 for ARR (n=294)(p=0.66), -0.14 for NNT (n=288)(p=0.73), -0.98 for RRR (n=292)(p=0.02), and +0.43 for LE (n=295)(p<0.0001). According to regression analysis of the change, people receiving RRR as the initial, single information changed their preference significantly when they were fully informed, while there was no change for the other formats, and change in preference for treatment was not influenced by age, sex, income or numeracy. While 27 persons were uncertain about their preferred information format, 106 (9%) preferred NNT, 436 (37%) RRR, 149 (13%) LE and 451 (39%) PR. The proportions that found the information very easy to understand were 72% (NNT), 67% (RRR), 61% (LE) and 82% (PR). There was no clear association between numeracy and preferred information format or comprehensibility. Conclusion: While ARR and NNT as separate format of information appear to result in similar decisions when compared to those of the “fully informed” individual, RRR may result in too optimistic view of the treatment and LE possibly too pessimistic. Pictorial representation scored best in terms of respondent preference and self-perceived comprehension.