Comparing treatment valuations between and within subjects in clinical trials: does it make a difference?

Valuations may be sensitive to biases, especially if elicited alongside randomized clinical trials. We investigated the construction of valuations assigned by women who entered a randomized clinical trial and were allocated to in-hospital or domiciliary monitoring. Women assigned valuations (0-10 visual analogue scale) to the strategy they had been allocated to and to the alternative strategy. Valuations were expressed as a between-subject difference (assigned by the women allocated to the respective strategies) and as within-subject differences (assigned by all women). Domiciliary monitoring was valued higher by the women allocated to that strategy (P = 0.10). In-hospital monitoring was valued higher by the women allocated to that strategy (P = 0.02). The average within-subject differences differed by allocated strategy (P <0.01). The within-subject valuation differences showed large variability between and within groups. An overrepresentation of women favoring domiciliary monitoring and asymmetric treatment experience inflated the average within-subject difference in the domiciliary group but deflated that difference in the in-hospital group. Neither the average between-subject difference nor the average within-subject differences are free of bias. Other study designs probably cannot prevent bias. Comparing within-subject and between-subject differences is instructive