Citation

Sirota M, Juanchich M, Petrova D, Garcia-Retamero R, Walasek L, Bhatia S. Med. Decis. Making 2018; 38(3): 366-376.

Affiliation

Department of Psychology, University of Pennsylvania, Philadelphia, PA, USA (SB).

Copyright

(Copyright © 2018, SAGE Publishing)

DOI

10.1177/0272989X17734203

PMID

29068246

Abstract

BACKGROUND: Previous research has shown that format effects, such as the "1-in-X" effect-whereby "1-in-X" ratios lead to a higher perceived probability than "N-in-N*X" ratios-alter perceptions of medical probabilities. We do not know, however, how prevalent this effect is in practice; i.e., how often health professionals use the "1-in-X" ratio.

METHODS: We assembled 4 different sources of evidence, involving experimental work and corpus studies, to examine the use of "1-in-X" and other numerical formats quantifying probability.

RESULTS: Our results revealed that the use of the "1-in-X" ratio is prevalent and that health professionals prefer this format compared with other numerical formats (i.e., the "N-in-N*X", %, and decimal formats). In Study 1, UK family physicians preferred to communicate prenatal risk using a "1-in-X" ratio (80.4%, n = 131) across different risk levels and regardless of patients' numeracy levels. In Study 2, a sample from the UK adult population ( n = 203) reported that most GPs (60.6%) preferred to use "1-in-X" ratios compared with other formats. In Study 3, "1-in-X" ratios were the most commonly used format in a set of randomly sampled drug leaflets describing the risk of side effects (100%, n = 94). In Study 4, the "1-in-X" format was the most commonly used numerical expression of medical probabilities or frequencies on the UK's NHS website (45.7%, n = 2,469 sentences).

CONCLUSIONS: The prevalent use of "1-in-X" ratios magnifies the chances of increased subjective probability. Further research should establish clinical significance of the "1-in-X" effect.

Language: en

Keywords

effect; format preference; ratio; risk communication; subjective probability; “1-in-X”