[영문]This paper describes an experiment to test the construct validity of contingent valuation, by eliciting women's valuations for the NHS cervical cancer screening programme. It is known that, owing to low levels of knowledge of cancer and screening in the general population, women both over-estimate the risk of disease and the efficacy of screening. The study is constructed as a randomised experiment, in which one group is provided with accurate information about cervical cancer screening, whilst the other is not. The first hypothesis supporting construct validity, that controls who perceive greater benefits from screening will offer higher valuations, is substantiated. Both groups are then provided with objective information on an improvement to the screening programme, and are asked to value the improvement as an increment to their original valuations. The second hypothesis supporting construct validity, that controls who perceive the benefits of the programme to be high already will offer lower incremental valuations, is also substantiated.