Dataset: Psychological defeat and self-efficacy among family caregivers of patients with cancer in Saudi Arabia

De-identified participant-level data (N = 225) underlying the manuscript "Psychological defeat and its association with self-efficacy among family caregivers of patients with cancer: a cross-sectional study from Saudi Arabia" (PLOS ONE, under review). The file includes item-level responses to the 48-item Psychological Defeat Scale and the 21-item Self-Efficacy Scale, subscale and total scores, four demographic variables (age group, gender, kinship, occupation), and a codebook. Data were collected at King Fahad Specialist Hospital, Dammam, Saudi Arabia, between 11 September 2025 and 30 January 2026 (ethics approvals: King Faisal University KFU-REC-2024-DEC-ETHICS2978; KFSH-D IRB EXT0463). No names, contact details, dates or free-text responses were collected.