Background Empirical studies of surrogate decision-making tend to assume that surrogates should make only a 'substituted judgement'—that is, judge what the patient would want if they were mentally competent.

Objectives To explore what people want in a surrogate decision-maker whom they themselves select and to test the assumption that people want their chosen surrogate to make only a substituted judgement.

Methods 30 undergraduate students were recruited. They were presented with a hypothetical scenario about their expected loss of mental capacity in the future and asked to answer some questions about their choice of surrogate. These data were analysed qualitatively using thematic content analysis.

Results Most respondents talked about choosing someone who was caring and competent in certain ways, giving interesting evidence for their judgements. Surprisingly few highlighted how well they thought their chosen surrogate knew their preferences and would be able to make a substituted judgement. Moreover, few specified that their chosen surrogate had similar attitudes and values to their own and so would make a similar decision to theirs in the circumstances presented. Some respondents also referred to the social role of their chosen surrogate or the social dynamics of their situation which influenced their choices, as well as to ideas of reciprocity and characteristics of honesty and loyalty.

Conclusion In the event that they lose mental capacity, many people will not select a surrogate to decide about medical treatments on their behalf solely on the basis that they expect their surrogate to make a substituted judgement.