Background: Telephone assessment of depression for research purposes is increasingly being used. The Patient Health Questionnaire 9-item depression module (PHQ-9) is a well-validated, brief, self-reported, diagnostic, and severity measure of depression designed for use in primary care (PC). To our knowledge, there are no available data regarding its validity when administered over the telephone.
Objective: The aims of the present study were to evaluate agreement between self-administered and telephone-administered PHQ-9, to investigate possible systematic bias, and to evaluate the internal consistency of the telephone-administered PHQ-9.
Methods: Three hundred and forty-six participants from two PC centers were assessed twice with the PHQ-9. Participants were divided into 4 groups according to administration procedure order and administration procedure of the PHQ-9: Self-administered/Telephone-administered; Telephone-administered/Self-administered; Telephone-administered/Telephone-administered; and Self-administered/Self-administered. The first 2 groups served for analyzing the procedural validity of telephone-administered PHQ-9. The last 2 allowed a test–retest reliability analysis of both self- and telephone-administered PHQ-9. Intraclass correlation coefficient (ICC) and weighted κ (for each item) were calculated as measures of concordance. Additionally, Pearson's correlation coefficient, Student's t-test, and Cronbach's α were analyzed.
Results: Intraclass correlation coefficient and weighted κ between both administration procedures were excellent, revealing a strong concordance between telephone- and self-administered PHQ-9. A small and clinically nonsignificant tendency was observed toward lower scores for the telephone-administered PHQ-9. The internal consistency of the telephone-administered PHQ-9 was high and close to the self-administered one.
Conclusions: Telephone and in-person assessments by means of the PHQ-9 yield similar results. Thus, telephone administration of the PHQ-9 seems to be a reliable procedure for assessing depression in PC.