In patients with major depressive disorder (MDD), the Patient Health Questionnaire-9 (PHQ-9) has demonstrated a strong correlation with the substantive scales of the Minnesota Multiphasic Personality Inventory-2-Restructured Form (MMPI-2-RF), including the broad Higher-Order EID-Emotional/Internalizing Dysfunction scale, as well as the RCd-Demoralization, RC7-Dysfunctional Negative Emotions, and NEGE-r-Negative Emotionality scales. Results of the study were published in the Journal of Clinical Psychology in Medical Settings.
Recognizing that the 40 psychopathology constructs evaluated by the MMPI-2-RF offer a useful map for establishing exactly what is being measured by the PHQ-9, the investigators sought to assess the PHQ-9 more precisely, taking into consideration the heterogeneous nature of MDD as a broad diagnostic category. Researchers examined a group of participants recruited from an undergraduate pool at a medium rural state comprehensive university in the southeastern United States. A total of 231 college student volunteers were enrolled in the study, all of whom completed the PHQ-9 and MMPI-2-RF as components of a greater research program. All the participants received credit in the college’s introductory psychology course.
There was a significant correlation between the PHQ-9 and the EID domain (r = 0.48) compared with thought and behavioral/externalizing dysfunction (r = 0.25 and 0.22, respectively). Within the EID domain, the correlation between the PHQ-9 and RCd-Demoralization (r = .59) was significantly higher than the correlations between the PHQ-9 and RC2-Low Positive Emotions (r = .33) and RC7-Dysfunctional Negative Emotions (r = .44). The correlation of the PHQ-9 with RC2-Low Positive Emotions was not one of the strongest associations, in spite of the fact that the PHQ-9 allegedly targets this particular feature of depression (anhedonia). In addition, significant correlations with the somatic (r = 0.55) and cognitive (r = 0.54) scales of the MMPI-2-RF were also reported.
Study limitations included a reliance on a college student sample. However, in light of the results of the study, the researchers concluded that it is critical to rethink the interpretation of the PHQ-9, as this measure is widely employed in primary care settings. They called for the development of new screening measures of “key behavioral health problems” that are tailored to the needs of primary settings.
In conclusion, the researchers noted that the scale may represent “general emotional distress and physical malaise” rather than depression, which may still require “professional intervention but not necessarily antidepressant medication.”
McCord DM, Provost RP. Construct validity of the PHQ-9 depression screen: correlations with substantive scales of the MMPI-2-RF. J Clin Psychol Med Settings. 2020;27(1):150-157.