Personalized versus standardized socially assistive robots for loneliness and depression reduction in older adults: study protocol for a three-arm randomized controlled trial

The global population is aging at an unprecedented rate, presenting substantial challenges to healthcare systems and social support networks. Loneliness and depression have emerged as critical public health concerns among older adults, associated with increased morbidity, mortality, and healthcare utilization. Socially assistive robots (SARs) represent a promising intervention, yet a fundamental question remains unresolved: whether the additional resources required for a personalized approach yield superior benefits compared to a more standardized interaction. The purpose of this study is to compare the efficacy of a personalized, co-designed robot interaction against a standardized, fixed robot interaction for reducing loneliness, depression, as well as improving self-agency and quality of life in older adults. This is a three-arm randomized controlled trial. The study will be conducted at a community center in Fuzhou, China, with 100 participants aged 65 + recruited from the facility. The participants will be randomly assigned to one of three conditions: (1) Co-designed robot (CL) group receiving a personalized robot interaction with a structured co-design ceremony; (2) Standard robot (SL) group interacting with an identical robot without personalization features; or (3) An attention-controlled usual care (CU) group. The intervention comprises 16 sessions (two weekly 20-minute sessions over eight weeks). The primary outcomes are loneliness and depressive symptoms. Secondary outcomes include general self-efficacy, quality of life, as well as staff and participants’ perceptions of the robot. Mechanism measures (i.e., engagement, self-disclosure) and manipulation checks (e.g., perceived personal role) will be employed to elucidate the underlying theoretical pathways. Data will be collected at baseline (T0), after the initial 2-week co-design period (T1), post-intervention (T2, Week 8), and at 1-month (T3) and 3-month (T4) follow-ups. The study participants or their proxy will provide written informed consent. The University Ethics Committee has approved the study (H20250560I). The results of the study will provide evidence of the efficacy of a co-design intervention regarding robotic pets as a psychosocial treatment for older adults in the long-term care facilities. Findings will be presented at scientific conferences and published in peer-reviewed journals. Clinical Trials Registry number NCT07102017, date registered 16/11/2025.