Investigating the PHQ-9 With Mokken Scale Analysis and Cognitive Interviews

Area of Science:

• Psychiatry
• Psychometrics

Background:

• The Patient Health Questionnaire-9 (PHQ-9) is widely used to measure depression severity in clinical and research settings.
• Validating assessment tools is crucial for accurate diagnosis and treatment monitoring.

Purpose of the Study:

• To evaluate the validity of the Icelandic version of the PHQ-9 sum score.
• To identify potential issues in the PHQ-9's psychometric properties and respondent comprehension.

Main Methods:

• Mokken scale analysis was performed on a primary care sample (n=618) to assess unidimensionality (Study I).
• Cognitive interviews were conducted with individuals with and without a history of depression (n=53) to explore response patterns (Study II).

Main Results:

• Mokken scale analysis indicated that PHQ-9 items lack sufficient unidimensionality for accurate depression severity ordering.
• Cognitive interviews revealed several issues related to how respondents interpret and use the PHQ-9 items.
• No significant differences in PHQ-9 usage or interpretation were found between individuals with and without a history of depression.

Conclusions:

• The PHQ-9 sum score requires cautious interpretation due to concerns with its psychometric properties and respondent understanding.
• Recommendations for revising the PHQ-9 scale are provided to enhance its measurement quality and clinical utility.