Background: Clinicians and researchers often have to rely on information from caregivers to assess patients with advanced cancer. This study aims to assess the validity (using patients' assessment as the gold standard) of caregiver reports of patient concerns and the roles of caregiver burden and positivity.
Methods: A total of 64 advanced cancer patient and informal caregiver dyads were recruited from regional palliative care services and interviewed. Patients' outcomes were assessed with both the patient and the caregiver version of the Palliative Outcome Scale (POS); caregiver burden and positivity were collected with the Zarit Burden interview (ZBI) and three questions on achievements and relationships. The agreement between patient- and caregiver-rated POS was measured with weighted kappa statistics. The roles of caregiver burden and positivity in POS agreement were studied with logistic regression controlling for potential confounders; adjusted odds ratios were estimated from the models.
Results: Agreement was substantial for pain, moderate for four items, fair for three items and slight for two items. Compared with patients self-ratings, caregivers described more problems with information given and sharing feelings and were less likely to assess the patient felt their life was worthwhile or felt good about themselves. Disagreement for three POS item ratings was significantly associated with higher caregiver burden: "feeling anxious"(OR: 4.5; 95%CI: 1.3 to 15.6), "life worthwhile"(OR: 12.4; 95%CI: 2.9 to 54.3) and "felt good" (OR: 7.7; 95%CI: 2.0 to 29.6). Caregivers with higher positivity scores were more likely to agree patients' rating of "felt good"(OR: 0.3; 95%CI: 0.1-0.9) but at increased risk of disagreeing about patient's "practical problems"(OR: 4.2; 95%CI: 1.1 to 16.6).
Conclusion: Caregiver burden and positivity affect their assessments, especially of psychological patient domains and whether patients assess their life as worthwhile. Awareness of this might help clinicians and researchers better interpret caregiver assessments.