Impact of family function on psychological distress and its threshold effect in informal caregivers of elderly people with dementia

The Circumplex model has been a subject of controversy. Our study aims to validate its curvilinear hypothesis by examining the relationship between family function and psychological distress in informal caregivers of people with dementia (PwD). If a curvilinear relationship is identified, it will provide empirical support for the Circumplex model. Conversely, if a linear relationship is found, the threshold effect can be further clarified, thereby offering a foundation for personalized psychological intervention strategies for caregivers at the family level. We recruited a total of 267 elderly PwD and their informal caregivers as research subjects. Using a self-designed questionnaire, the Kessler Psychological Distress Scale, and the Family Adaptation and Cohesion Evaluation Scales to detect curvilinear or linear relationships, perform smooth curve fitting, and conduct threshold effect analysis. Between-group differences were significant across the three family types (P = 0.001), as were within-group differences among the four family function types (P = 0.000, P = 0.000). A negative correlation was observed between family function and psychological distress. When the family score was ≤ 140, the psychological distress score decreased as the family function score increased (P < 0.001). However, when the family function score was > 140, the level of psychological distress remained unchanged (P = 0.552). The better the family function of caregivers, the less likely adverse psychological conditions are to occur. A family function score of 140 can serve as a node for assigning tiered, individualized interventions.