The time trade-off (TTO) is one of the most widely used health state valuation methods and was recently used to develop a set of values for the EQ-5D descriptive system from 3000 members of the UK general population. However, there is currently very little understanding of precisely what determines responses to TTO questions. The data that were used to generate this set of values are ideal for addressing this question since they contain a plethora of information relating to the respondents and their cognition during the TTO exercise. A particularly useful characteristic of this dataset is the existence of visual analogue scale (VAS) valuations on the same states for the same respondents. The results suggest that age, sex and marital status are the most important respondent characteristics determining health state valuations. The VAS valuations were found to add very little to the explanatory power of the models.