The usefulness of depression scales for patients with cancer based on item response theory (IRT) and computer adaptive testing (CAT) has not yet been fully explored. This study thus aimed to develop an IRT-based tool for measuring depression in patients with cancer. We analyzed data from 393 patients with cancer from four tertiary centers in Japan who had not received psychiatric treatment. They answered 62 questions across five categories regarding their psychiatric status over the previous week. We selected 28 items that satisfied the assumptions of IRT, fitted a graded response model to these items, and performed CAT simulations. The CAT simulation used an average of 6.96 items and showed a Pearson’s correlation coefficient of 0.916 (95% confidence interval, 0.899–0.931) between the degree of depression estimated by simulation and that estimated using all 28 items. The measurement precision of CAT with only four items was superior to that of the estimation using the calibrated Patient Health Questionnaire-9. These results imply that this scale is useful and accurate for measuring depression in patients with cancer.
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