Of 3,775 eligible youth, 2291 (60.7%) completed the brief survey (). Twelve percent of youth (N=281) screened positive for possible depression with a PHQ2 ≥ 3 and 88% screened negative for depressive symptoms. 499 youth were invited to participate in the full baseline assessment of whom 444 (89%) consented and both the parent and child completed the baseline survey. Two youth who met DSM-IV criteria for bereavement were removed from the analytic sample resulting in a final sample of 442 youth for the current analysis.
Recruitment for Adolescent Health Study
Study participants were predominantly female (60%), white (71%) and from urban regions (83%). The mean age of participants was 15.3 years (SD = 1.2 years). The median household income for neighborhoods in which subjects lived was $57,442 (SD = $18,293) and 86% of youth had one or more parents who had at least some exposure to higher education. Seven percent of youth were enrolled in a public assistance insurance plan.
shows the distribution of scores for each of the individual PHQ-2 items as well as for the full PHQ-2 score by depression status on DISC-IV (major depression, intermediate depression, or no depression). Youth meeting criteria for major depression had significantly higher total scores on the PHQ-2. Youth with “intermediate depression” on the DISC-IV were most likely to report symptoms several days but not nearly every day. Youth with no depression diagnosis were most likely to report no symptoms. When the sensitivity and specificity of each individual item in the PHQ-2 was examined neither individual item performed better than the two combined. This is supported by the significantly greater area under the curve for the PHQ-2 in comparison with either item [Chi-square, df = 2 = 39.97, p < .001].
Frequency distribution of depressed mood and anhedonia items and PHQ-2 score
shows the test characteristics of the PHQ-2 using the PHQ-9 and DISC-IV as gold standards. The optimal cut-point for maximizing sensitivity of the PHQ-2 without loss of specificity was a score of 3 or greater. At this cut-point, the PHQ-2 had a sensitivity of 96.2% for detecting youth with probable major depression by PHQ-9 criteria and of 73.7% for detecting youth with major depression on the DISC-IV. The specificity was 82.3% for detecting youth with probable major depression on the PHQ-9 and 75.2% for detecting youth with major depression on the DISC-IV. The positive predictive value was 42% for detecting probable major depression on the PHQ-9 and 11.8% for the DISC-IV. On ROC analysis () the area under the curve for detecting major depression was 0.84 (0.75 – 0.92) using the DISC-IV diagnosis as a gold standard and 0.95 (0.93–0.97) using the PHQ-9 diagnosis as a gold standard.
Sensitivity and Specificity of the PHQ-2
ROC curve plot for the PHQ2 using the DISC-IV as a gold standard
Youth with a PHQ-2 of ≥3 compared to those with <3 had significantly higher scores for functional impairment as measured by the Columbia Impairment Scale, as well as parent-reported psychosocial impairment as measured by the Pediatric Symptom Checklist (). Additionally, parental reports of internalizing symptoms were significantly higher for this group.
Item 9 of the PHQ-9 inquires how often the respondent is “thinking that you would be better off dead or that you want to hurt yourself in some way.” Sixteen youth indicated that they had these thoughts “more than half the days” or “nearly every day.” Of these 16 youth, 13 (81%) had a PHQ-2 score of ≥3, while three did not.
The false positive rate, calculated as 1-specificity, was approximately 25% when using the DISC-IV as a gold standard or 18% if using the PHQ-9 as a gold standard. To better understand the characteristics of youth with false positives, we examined the association between having a false positive PHQ-2 and having intermediate depression or a positive screening test for another disorder (anxiety or externalizing disorder). Among adolescents with PHQ-2 scores ≥3 but no DISC-IV diagnosis for major depression (N = 105), 23.3% had a intermediate depression on the DISC-IV, 14.7% had major depression in the past year but not in the prior month, 26.2% had elevated externalizing disorder symptoms (PSC-17 externalizing scale score ≥7), and 55.2% had clinically significant anxiety symptoms (SCARED score ≥3). Taken together, 76.2% of the false positive group had at least one of the four indications we examined: 39.0% had one, 32.4% had two, and 4.8% had three of the four indications.