Practical Mental Health Assessment in Primary Care

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Original Research

Practical Mental Health Assessment in Primary Care

J Fam Pract. 2000 July;49(7):614-621

References

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Results

Validity Studies

Mood and Anxiety Disorders. The research subjects were 203 health maintenance organization (HMO) patients referred by their physicians or self-referred for a first-time mental health consultation. None were receiving mental health treatment at the time of the study. Patients scheduled for first-time mental health consultations were recruited by telephone during the week before the consultation and were paid $25 for participation. Approximately 60% of those contacted agreed to participate. One patient who appeared to have a psychotic disorder was excluded from the sample. The sample was two thirds women, with a mean age of 41.39 years (standard deviation [SD]=11.69). The subjects completed an assessment protocol that included the QPD Panel, relevant modules of the SCID structured psychiatric interview, and the Hamilton Depression Inventory.20 Administration order was randomized. SCID diagnostic interviews were conducted by mental health professionals with master’s or doctorate degrees who were trained in the administration of the SCID and blind with respect to all other study data.

[Table 2] shows indexes of agreement between QPD Panel diagnoses and SCID structured interview diagnoses. The first 2 columns report sensitivity (proportion of patients with a positive SCID diagnosis correctly identified by the QPD Panel) and specificity (proportion of patients without a SCID diagnosis correctly identified by the QPD Panel). Sensitivity was good to excellent for all diagnoses, ranging from 69% (for OCD) to 81% (for major depression). Specificities were uniformly high, ranging from 90% to 97%, indicating that the test seldom made false-positive diagnoses (ie, diagnoses not confirmed by the SCID). The third column of Table 2 reports k coefficients, which provide an index of agreement between the QPD and SCID diagnoses, correcting for agreement due to chance.²¹ The k coefficients were good to excellent for all diagnoses, ranging from a low of .64 for OCD to a high of .79 for major depression.* The last 2 columns of Table 2 list the prevalence rates for each diagnosis, as determined by the QPD Panel and by the SCID. Prevalence rates were comparable for both instruments, suggesting that neither instrument had a systematic tendency to overdiagnose or underdiagnose any disorder.

Alcohol and Substance Abuse. The QPD Panel includes a 14-item alcohol/substance abuse scale. All patients answer 5 of the questions; the remaining questions are presented only when previous responses suggest abuse. The numeric alcohol/substance abuse score is derived by summing true responses to the scale items, so the scale has a possible range of 0 to 14. The goals of this study were to evaluate the diagnostic accuracy of the scale and establish the optimal cut-point for making a diagnosis. The study evaluated the QPD Panel’s ability to distinguish between patients known to suffer from alcohol or substance abuse and healthy control patients.

The research subjects were 159 patients enrolled in an HMO health plan; 70.8% were women, with a mean age of 41.9 years (SD=12.25). Forty-six of the patients had received a definitive diagnosis of alcohol or substance abuse by their physicians or by a mental health professional and had been referred to a chemical dependency clinic for treatment (chemical dependency sample); they completed the QPD Panel as part of the chemical dependency clinic intake procedure. The remaining 113 patients were control patients who completed the QPD Panel during routine primary care office appointments (control sample).

[Table 3] reports the sensitivity, specificity, and k coefficients obtained using 4 scale cut-points. The first row presents the validity coefficients when a scale score of 1 or higher was treated as a positive diagnosis; the second row presents the validity coefficients when a scale score of 2 or higher was treated as a positive diagnosis; and so on. The scale achieved maximum diagnostic accuracy when a score of 2 or higher was treated as a positive diagnosis (Table 3, row in boldface), with a resulting sensitivity of 98% and specificity of 92%.

Convergent Validity. To establish convergent validity, we examined correlations between selected QPD Panel severity scales (numeric scores) and established, well-validated measures. Correlations were obtained in a variety of patient and community samples, with sample numbers ranging from 113 to 215.* The QPD Panel depression scale correlated highly with the Beck Depression Inventory²² (BDI, r=.80); the Hamilton Depression Inventory20 (r=.87); the Center for Epidemiological Studies Depression (CES-D) Scale²³ (r=.79); and the Zung Self-Rating Depression Scale²⁴ (r=.78). The QPD Panel anxiety scale correlated highly with the Spielberger State-Trait Anxiety Inventory²⁵ (r=.67) and the anxiety subscale of the Symptom Checklist-90 (SCL-90)²⁶ (r=.76). The QPD Panel somatization scale correlated highly with the somatization subscale of the Symptom Checklist 28 (SCL-28), r=.59. All correlations are statistically significant (Ps <.001) and near the upper limits allowed by the respective scale reliabilities, indicating strong convergent validity.