There is no scientific consensus on the optimal specification of the time trade-off (TTO) task. As a consequence, studies using TTO to value health states may share the core element of trading length of life for quality of life, but can differ considerably on many other elements. While this pluriformity in specifications advances the understanding of TTO from a methodological point of view, it also results in incomparable health state values. Health state values are applied in health technology assessments, and in that context comparability of information is desired. In this article, we discuss several alternative specifications of TTO presented in the literature. The defining elements of these specifications are identified as being either methodological, procedural or analytical in nature. Where possible, it is indicated how these elements affect health state values (i.e., upward or downward). Finally, a checklist for TTO studies is presented, which incorporates a list of choices to be made by researchers who wish to perform a TTO task. Such a checklist enables other researchers to align methodologies in order to enhance the comparability of health state values.

Most psychological factors showed stability up to 6 months post-discharge. Purpose in life, acceptance cognitions, self-efficacy, and mastery showed more variability and seem to be most promising as targets for interventions, which may lead to an improvement in mental health in persons with spinal cord injury.

Almost all respondents need interviewer help. This may have implications for the validity of interviewer-based TTO elicitations when social acceptability bias is an issue or with explicit hypothesis and the interviewer is not blinded. The FAQ list can be used to standardize interviewer help or as a help function in a web-based TTO.

Patients' health state valuations change over time, over and above the change expected by the rehabilitation process, and this change is partly explained by adaptation. Experience with a chronic illness did not lead to change in valuations of hypothetical health states.