Development of a diverse set of standard short forms based on the EORTC CAT Core item banks

The European Organisation for Research and Treatment of Cancer (EORTC) Quality of Life Group has developed item banks covering the 14 domains of the EORTC QLQ-C30 quality of life questionnaire. These allow for dynamic assessment and for forming population/study specific static short forms. To simplify selection of relevant short forms, we here present a portfolio of standard short forms with measurement properties optimized for different populations.

For each domain, a brief and a long version were constructed for each of three populations having mild, moderate, and severe symptoms, respectively. The most informative items were prioritised while also taking content into consideration. All short forms included at least one QLQ-C30 item. The measurement precision/power of the short forms was compared to the corresponding QLQ-C30 scales using simulations.

In total, 84 short forms were constructed. The brief versions included 3-5 items each, the long versions 5-9 items. Estimated sample size savings using the suggested short forms while maintaining the same power as with the QLQ-C30 ranged 3-50% across domains with median savings of 19% (brief versions) and 28% (long versions), respectively.

The suggested short forms allow for simple selection of items particularly relevant for patients with mild, moderate, or severe symptoms, respectively. They facilitate the use of smaller samples without loss of power compared to the QLQ-C30 scales. The suggested short forms may be used as they are or adapted to the specific aims of individual studies/settings.