International application of PROMIS computerized adaptive tests: US versus country-specific item parameters can be consequential for individual patient scores.

PROMIS offers computerized adaptive tests (CAT) of patient-reported outcomes, using a single set of US-based IRT item parameters across populations and language-versions. The use of country-specific item parameters has local appeal, but also disadvantages. We illustrate the effects of choosing US or country-specific item parameters on PROMIS CAT T-scores. Simulations were performed on response data from Dutch chronic pain patients (n = 1110) who completed the PROMIS Pain Behavior item bank. We compared CAT T-scores obtained with (1) US parameters; (2) Dutch item parameters; (3) US item parameters for DIF-free items and Dutch item parameters (rescaled to the US metric) for DIF items; (4) Dutch item parameters for all items (rescaled to the US metric). Without anchoring to a common metric, CAT T-scores cannot be compared. When scores were rescaled to the US metric, mean differences in CAT T-scores based on US vs. Dutch item parameters were negligible. However, 0.9%-4.3% of the T-score differences were larger than 5 points (0.5 SD). The choice of item parameters can be consequential for individual patient scores. We recommend more studies of translated CATs to examine if strategies that allow for country-specific item parameters should be further investigated.

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