The Social Difficulties Inventory (SDI): development of subscales and scoring guidance for staff

To develop subscales for clinical use of the Social Difficulties Inventory (SDI) with score interpretation guidance for use in routine oncology practice.

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 were pooled from three studies investigating psychometrics and clinical utility of the SDI-21.

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.

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.

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.