Depression is highly comorbid with alcohol and drug problems, resulting in greater impairment, reduced treatment adherence and poor outcomes. Little evidence exists to support the use of mental health screening tools in routine addiction treatment. This study tested the validity and reliability of PHQ-9 and PHQ-2 as depression case finding tools in an outpatient drug treatment sample in the United Kingdom.
A sample of 103 patients took part in diagnostic assessments using CIS-R and completed brief screening questionnaires. A subgroup of 60 patients completed retests after 4
weeks. Diagnostic results were compared to brief measures using receiver operating characteristic (ROC) curves. Psychometric properties were also calculated to evaluate the validity and reliability of self-completed questionnaires.
A PHQ-9 score ≥12 had a sensitivity of 81% and specificity of 75% for major depression, also displaying good retest reliability (intra-class correlation, 0.78) and internal consistency (Cronbach's alpha, 0.84). PHQ-2 had 68% sensitivity and 70% specificity, with more modest retest reliability (0.66) and internal consistency (0.64).
Diagnostic interviews did not consider the temporal sequencing of the onset of drug use and mental health problems.
PHQ-9 is a valid and reliable depression screening tool for drug and alcohol users. The brevity and ease of administration of self-completed questionnaires make them useful clinical tools in addiction services commonly encountering a high prevalence of depression.
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