Aims
Computerised adaptive test (CAT) provides individualised patient reported outcome measurement while retaining direct comparability of scores across patients and studies. Optimal CAT measurement requires an appropriate CAT-setting, the set of criteria defining the CAT including start item, item selection criterion, and stop criterion. The European Organisation for Research and Treatment of Cancer (EORTC) CAT Core allows for assessing the 14 functional and symptom domains covered by the EORTC QLQ-C30 questionnaire. The aim was to present a general approach for selecting CAT-settings and to use this to develop a portfolio of standard settings for the EORTC CAT Core optimised for different purposes and populations.

Methods
Using simulations, the measurement properties of CATs of different length and precision were evaluated and compared allowing for identifying the most suitable settings. All CATs were initiated with the most informative QLQ-C30 item. For each domain two fixed-length and two fixed-precision standard CATs were selected focusing on efficiency (brief version) and precision (long), respectively.

Results
The brief fixed-length CATs included 3–5 items each while the long versions included 5–8 items. The fixed-precision CATs aimed for reliability of 0.65–0.95 (brief versions) and 0.85–0.98 (long versions), respectively. Median sample size savings using the CATs compared to the QLQ-C30 scales ranged 20%-31%, although savings varied considerably across the domains.

Conclusion
The EORTC CAT Core standard settings simplify selection of relevant and appropriate CATs. The CATs prioritise either brevity and efficiency or precision, but all provide increased measurement precision and hence, reduced sample size requirements compared to the QLQ-C30 scales. The CATs may be used as they are or modified to accommodate specific requirements.