Citizen participation in decision making has been widely lauded as a method for improving societal outcomes. Deliberative discussion, in particular, is believed to be more transformative than a mere aggregation of individual preferences, leading to more socially optimal decision making and behavior. I report the results from a laboratory experiment with 570 subjects in Nairobi, directly testing the effect of participation in deliberative group decision making on collective outcomes. Participants engage in a group task to earn compensation toward a shared group fund. Randomly assigned treatments vary according to whether decision making over the task to be completed involves: (1) external assignment; (2) non-deliberative majority voting; or (3) consensus through deliberative discussion. I find that deliberation improves collective decision making. Deliberation is also associated with changes in preferences, greater agreement with decision outcomes, and greater perceived fairness. Evidence for behavior change is weaker, but there is some support for further research into the relationship between preference change and behavior change.

Robert Sugden has suggested a normative standard of freedom as ‘opportunity’ that is supposed to help realign normative economics – with its traditional rational choice orientation – with behavioural economics. While allowing preferences to be incoherent, he wants to maintain the anti-paternalist stance of orthodox welfare economics. His standard, though, presupposes that people respond to uncertainty about their own future preferences by dismissing any kind of self-constraint. We argue that the approach lacks psychological substance: Sugden's normative benchmark – the ‘responsible person’ – can hardly serve as a convincing role model in a contractarian setting. An alternative concept is introduced, and some implications are briefly discussed.