Aims: To develop subscales for clinical use of the Social Difficulties Inventory (SDI) with score interpretation guidance for use in routine oncology practice.
Background: Patient-reported outcome measures are used increasingly in cancer care but successful implementation is dependent on a combination of sound psychometrics, guidance on clinical meaning and good clinical judgement. The SDI, a 21-item instrument (SDI-21) developed for use in cancer care, demonstrated good psychometric properties. Rasch analysis of the SDI resulted in a 16-item interval scale of Social Distress (SD-16), which allowed for establishment of some clinical utility guidance but further work was required to optimise meaningful interpretation in clinical practice.
Data sources: Data were pooled from three studies investigating psychometrics and clinical utility of the SDI-21.
Statistical analyses: Common factor analysis was undertaken on SD-16 items. Subscales were derived from the resulting factors and calculated by summing the scores of associated items. Subscale reliability was evaluated using Cronbach's α.
Results: There were 652 participants. A three-factor model explaining 53.3% of the variance was extracted forming the basis of the subscales: Everyday living, Money matters and Self and others. Subscale reliability was good. In a clinical setting, a 2-point change in subscale score could be interpreted as a clinically meaningful difference.
Conclusion: The development of three subscales and clinically significant difference scores for the SD-16, combined with the previously developed cut-off points, improves the clinical utility of the SDI-21 when assessing social issues in oncology care.