Beliefs About Dementia: Development and Validation of the Representations and Adjustment to Dementia Index (RADIX)

The Self-Regulation Model (SRM) identifies that the beliefs people hold about an illness can influence their responses to that illness. Although there are generic measures of illness representations, there is a need for a brief tailored measure to use with people with dementia. The aim of this study was to develop and validate a brief measure called the Representations and Adjustment to Dementia Index (RADIX). The RADIX contains questions on the SRM elements: Identity, Cause, Timeline, Control, and Consequences.

The RADIX validation was conducted with a sample of 385 community-dwelling people with mild to moderate dementia who were taking part in the IDEAL cohort study. Test-retest reliability was conducted over a 4-week period with a separate sample of 20 people with dementia.

The validation process resulted in a reduction in the number of items in the Timeline, Control, and Consequences items. The resulting RADIX demonstrated good acceptability, internal reliability, and test-retest reliability. All the RADIX items had low missing data, indicating good acceptability. The factor analysis confirmed that the Consequences items formed two subscales (practical and emotional consequences) that had Cronbach's α of 8 and 0.91 respectively. Test-retest reliability indicated that the Identity, Timeline, and Control items had moderate reliability and the practical and emotional consequences scales had good reliability.

The RADIX demonstrates acceptable psychometric properties, proves to be a useful measure for exploring people's beliefs about dementia, and could aid the provision of tailored information and support to people with dementia.