We compare two settings for administering time trade-off (TTO) tasks in computer-assisted interviews (one-to-one, interviewer-led versus group, self-complete) by examining the quality of the data generated in pilot studies undertaken in England and the Netherlands. The two studies used near-identical methods, except that in England, data were collected in one-to-one interviews with substantial amounts of interviewer assistance, whereas in the Netherlands, the computer aid was used as a self-completion tool in group interviews with lesser amounts of interviewer assistance. In total, 801 members of the general public (403 in England; 398 in the Netherlands) each completed five TTO valuations of EQ-5D-5L health states. Respondents in the Netherlands study showed a greater tendency to give 'round number' values such as 0 and 1 and to complete tasks using a minimal number of iterative steps. They also showed a greater tendency to skip the animated instructions that preceded the first task and to take into account assumptions that they were specifically asked not to take into account. When faced with a pair of health states in which one state dominated the other, respondents in the Netherlands study were more likely than those in the England study to give a higher value to the dominant health state. On the basis of these comparisons, we conclude that the one-to-one, interviewer-led setting is superior to the group, self-complete setting in terms of the quality of data generated and that the former is more suitable than the latter for TTO studies being used to value EQ-5D-5L.