Responses to the 16-item, clinician-rated Quick Inventory of Depressive Symptomatology (QIDS-C16)1-3 in patients with bipolar disorder and in patients with major depressive disorder (MDD) were recently evaluated.4 Results obtained in these two patient populations were similar in terms of internal consistency reliabilities and the relations of items to the scale as a whole, using both classical test theory (CTT) and item response theory (IRT). In particular, the correlations between individual items and total score were the same in both MDD and bipolar disorder groups. At baseline, depressed patients obtained the highest self-rated Quick Inventory of Depressive Symptomatology (QIDS-SR16) scores, and manic patients obtained the lowest scores. These findings are consistent with use of the QIDS-C16 to evaluate depression in both bipolar disorder and MDD patients.
This study seeks to extend the construct validity of the previous findings relative to the QIDS-C16 and QIDS-SR16 by examining a different sample of outpatients with bipolar disorder. This report generally contrasts bipolar disorder patients who were classified as depressed or euthymic. For some analyses, patients in the manic and mixed phases were combined due to small sample sizes.
This study relied on archived data from the Stanley Medical Research Institute (SMRI; formerly the Stanley Foundation Bipolar Network) and included the first 141 consecutively enrolled outpatients with bipolar disorder. Details are fully described elsewhere.5,6 In brief, patients volunteered for a naturalistic follow-up study and all patients provided written informed consent. During this early phase of SMRI, patients were recruited at four United States sites (Los Angeles, Dallas, Cincinnati, Bethesda) and one European site (Utrecht). Clinical state and medications were prospectively assessed at monthly visits, and medication changes were made as needed to control symptoms and side effects. Raters at all sites were interrater reliable on the rating scales, including the Young Mania Rating Scale and 30-item Inventory of Depressive Symptomatology–Clinician-rated. Diagnostic evaluations were conducted by trained clinicians using the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition.7 All diagnoses were based on DSM-IV-Text Revision.8
Clinicians completed the National Institutes of Mental Health Daily Life Chart (LCM)9 at each visit based on patients’ ratings and interviews. The LCM covers a 1-month period and provides a visual method of tracking patients’ mood at each visit. Patients rated daily manic and depressive symptoms, listed medications taken during the past month, and recorded any other relevant non-mood symptoms if applicable. Patients recorded the “daily” severity of their mood symptoms using a 10-point scale of euthymic (0) to low-moderate (5) to severe (10) dysfunction. Mania ratings are coded as positive (0–10) and depression ratings are coded as negative (0 to -10).
The primary strategy was to compare patient groups defined by their illness phase at exit using standard psychometric procedures. As with our prior studies, IRT analyses were also conducted but will not be presented here, for brevity. Those interested in these latter results may contact the first author. Illness phases included depressed, euthymic, or, in lesser numbers, manic/mixed. The CTT analysis evaluated domain means, domain standard deviations, and item (domain) to total correlations (rit) obtained for each of the nine QIDS domains (Table 1), and the mean, standard deviation, and internal consistency (coefficient a) obtained for each scale as a whole.
Treatment effects over time were evaluated for each domain and for the total score by dividing the mean difference between baseline and exit by the standard deviation of this difference, ie, as Cohen’s d values. Response to treatment, defined as a >50% reduction in QIDS-C16 or QIDS-SR16 scores at exit relative to baseline, and remission, defined as an exit QIDS-C16 or QIDS-SR16 of <5, were examined as a function of phase of illness. These analyses were conducted separately for each of the nine pairings at baseline and exit for each phase (depressed, euthymic, and manic/mixed in each instance). Finally, effect sizes were obtained for individual domains.
At baseline, the phases of illness were depressed=61, euthymic=30, manic=14, and mixed=36. At exit, the illness phases were depressed=50, euthymic=52, manic=15, and mixed=24. The sample was 53% female, with a mean age of 46.2 years (standard deviation [SD]=13.5 years). The mean age at the onset of bipolar disorder was 23.1 years (SD=10.9). Overall, 93.7% were Caucasian.
Across all patients (n=141), the QIDS-C16 and QIDS-SR16 total scores were highly correlated (.89 at baseline and .92 at exit). Consequently, the results for these two measures were highly similar even though they will be reported separately. The following results focus only on the exit data, except where noted.
Table 1 contains the item means and SDs, scale mean and SDs, and coefficients a for depressed and euthymic patients at exit. Not surprisingly, depressed phase patients had substantially higher mean scores than euthymic patients on both scales, t(100)=9.72 and 8.72 for the QIDS-C16 and QIDS-SR16, respectively, P<.01. In general, the rank ordering of the nine domains within each group was highly similar, even though depressed patients obtained higher mean scores than euthymic patients. For example, sleep disturbances are reported with relatively high frequency in both groups, and thoughts of death or suicide are reported with relatively low frequency by both groups. As a result, the profiles of domain means are essentially parallel (Figures 1 and 2).
Finally, internal consistency reliabilities (coefficients a) were higher among depressed (a=.84 for both measures) than euthymic patients (a=.65 and .72 for the QIDS-C16 and QIDS-SR16, respectively). These differences largely reflect the greater variability among depressed than euthymic patients.
Scale Effect Sizes, Scale Response Rates, and Scale Remission Rates
Table 2 contains treatment effect sizes, response rates, and remission rates as a joint function of baseline and exit phase, with manic and mixed phases pooled into one group. Treatment effects are defined as the difference between domain and overall scale means divided by the standard deviation of this difference for depressed and euthymic patients. Because baseline QIDS-C16 and QIDS-SR16 scores were not extremely elevated for many patients, it was not uncommon for a patient to meet the criterion for remission but not response. Transitions from euthymic to depressed and from euthymic to manic/mixed occurred too infrequently to permit meaningful summary results.
The main points to note are that patients who were euthymic at exit had improved more than manic/mixed patients at exit, and the manic/mixed patients at exit had improved more than depressed patients at exit. These findings indicate that the QIDS-SR16 has properties that one would expect of it.
Domain Effect Sizes
Table 3 contains the effect sizes for individual domains, again as a function of baseline and exit phase. Note that patients who remained in a depressed phase showed little change. In contrast, patients who went from the depressed to euthymic phase showed the largest change in the two most central symptoms—sad mood and general interest. However, this was not true of patients who went from the depressed to the manic/mixed phase. Their largest change was in energy level (as might be expected). Patients who stayed in the euthymic phase or the manic/mixed phase, and those who went from the mixed/manic to the depressed phase changed relatively little in terms of QIDS-C16 or QIDS-SR16 total scores. Finally, those who went from the manic/mixed phase to a euthymic phase showed a moderate improvement in several categories.
The psychometric properties of both the QIDS-C16 and QIDS-SR16 in this sample of bipolar outpatients are similar to the scale properties found in prior MDD samples10 and in a separate sample of bipolar disorder patients.4 Item/total correlations were lowest for appetite and sleep in depressed phase patients. Coefficient a was .84. For patients whose phases of illness were defined by the LCM method blind to the QIDS-SR16 ratings, euthymic patients had far less depressive symptomatology by QIDS-SR16 (mean=3.7+3.2) than the depressed phase patients (11.9+6.0). IRT parameter estimates led to the same general conclusions. In addition, group differences between depressed and euthymic patients were meaningful; eg, depressed patients had the higher observed means than euthymic patients, and the scale was reliable when the group variability permitted. These results suggest that the QIDS-C16 and QIDS-SR16 are both suitable for use with bipolar patients in these phases.
The availability of a depression rating that focuses only on the diagnostic symptom domains that define a major depressive episode and that can be reliably used as either a self-report or a clinician rating has clear practical advantages over one that requires clinician time. We have previously shown in a series of studies3,10-13 that the QIDS-SR16 and the QIDS-C16 have sufficiently reliable and equivalent properties (including item and scale total score effects sizes) that for patients with nonpsychotic MDD the self-report is a sensitive and reliable indicator of symptom severity and change with treatment. This report adds to the evidence4 that a similar conclusion may be drawn when these scales are used in bipolar disorder patients.
Other self-reports have been found to be of utility in MDD, including the Patient Health Questionnaire,14 the Beck Depression Inventory-II,15 and the Carroll Rating Scale.16 However, there has been little work done using these scales in bipolar disorder patients. The relatively few exceptions include Das and colleagues,17 Kumar and colleagues,18 and Feinberg and colleagues.19 However, all three scales are likely to perform well given their psychometric properties in MDD patients.
Since clinically we may not know which of our current MDD patients will develop bipolar disorder over time, it is most convenient to employ a depressive symptom scale that has demonstrated validity and sensitivity in both conditions. The QIDS-C16 and QIDS-SR16 are available at www.ids-qids.org; the paper-and-pencil form is in the public domain and multiple translations with careful back translations are available. Additional work is needed to compare both versions of the QIDS to other clinician ratings (eg, the Montgomery Äsberg Depression Rating Scale; the Hamilton Rating Scale for Depression) in patients with MDD.
A primary limitation of this study is the small sample size, especially for some comparisons. In addition, the relatively small numbers of manic and mixed phase patients forced us to pool two groups that may not be entirely comparable. Specifically, the self-report version provides an easy-to-use tool for practitioners. One possible reflection of this pooling and small sample size may be found in Table 3 where the remission rates for patients who were euthymic at baseline and exit (63%) was only slightly greater than the remission rates for patients who were euthymic at baseline and mixed or manic at exit (58%). A second limitation is that we do not know if the utility of self-report found with bipolar patients in general would hold in a sample of extremely psychotic patients.
Both the QIDS-C16 and QIDS-SR16 appear to have sufficiently acceptable psychometric properties to be of value to clinicians and researchers who are managing patients with bipolar disorder. Specifically, the self-report version provides an easy-to-use tool for practitioners. CNS
1. Rush AJ, Carmody TJ, Reimitz PE. The Inventory of Depressive Symptomatology (IDS): clinician (IDS-C) and self-report (IDS-SR) ratings of depressive symptoms. Int J Methods Psychiatr Res. 2000;9:45-59.
2. Rush AJ, Trivedi MH, Ibrahim HM, et al. The 16-Item Quick Inventory of Depressive Symptomatology (QIDS), clinician rating (QIDS-C), and self-report (QIDS-SR): a psychometric evaluation in patients with chronic major depression. Biol Psychiatry. 2003;54(5):573-583. Erratum p. 585.
3. Trivedi MH, Rush AJ, Ibrahim HM, et al. The Inventory of Depressive Symptomatology, Clinician Rating (IDS-C) and Self-Report (IDS-SR), and the Quick Inventory of Depressive Symptomatology, Clinician Rating (QIDS-C) and Self-Report (QIDS-SR) in public sector patients with mood disorders: a psychometric evaluation. Psychol Med. 2004;34(1):73-82.
4. Bernstein IH, Rush AJ, Suppes T, et al. A psychometric evaluation of the clinician-rated Quick Inventory of Depressive Symptomatology (QIDS-C16) in patients with bipolar disorder. Int J Methods Psychiatr Res. 2009;18(2):138-146.
5. Leverich GS, Nolen WA, Rush AJ, et al. The Stanley Foundation Bipolar Treatment Outcome Network. I. Longitudinal methodology. J Affect Disord. 2001;67(1-3):33-44.
6. Suppes T, Leverich GS, Keck PE, et al. The Stanley Foundation Bipolar Treatment Outcome Network. II. Demographics and illness characteristics of the first 261 patients. J Affect Disord. 2001;67(1-3):45-59.
7. First MB, Spitzer RL, Gibbon M, Williams JBW. Structure Clinical Interview for DSM-IV TM Disorders (SCID I), Clinician Version. Washington, DC: American Psychiatric Publishing, Inc.; 1997.
8. Diagnostic and Statistical Manual of Mental Disorders. 4th ed, text rev. Washington DC: American Psychiatric Press; 2000.
9. Leverich GS, Post RM. Life charting of affective disorders. CNS Spectr. 1998;3:21-37.
10. Bernstein IH, Rush AJ, Carmody TJ, Woo A, Trivedi MH. Clinical vs. self-report versions of the Quick Inventory of Depressive Symptomatology in a public sector sample. J Psychiatr Res. 2007;41(3-4):239-246.
11. Rush AJ, Trivedi MH, Carmody TJ, et al. Self-reported depressive symptom measures: sensitivity to detecting change in a randomized, controlled trial of chronically depressed, nonpsychotic outpatients. Neuropsychopharmacology. 2005;30(2):405-416.
12. Rush AJ, Bernstein IH, Trivedi MH, et al. An evaluation of the Quick Inventory of Depressive Symptomatology and the Hamilton Rating Scale for Depression: a Sequenced Treatment Alternatives to Relieve Depression trial report. Biol Psychiatry. 2006;59(6):493-501. Epub 2005 Sep 30.
13. Rush AJ, Carmody TJ, Ibrahim HM, et al. Comparison of self-report and clinician ratings on two inventories of depressive symptomatology. Psychiatr Serv. 2006;57(6):829-837.
14. Kroenke K, Spitzer RL, Williams JB. The PHQ-15: validity of a new measure for evaluating the severity of somatic symptoms. Psychosom Med. 2002;64(2):258-266.
15. Beck AT, Steer RA, Brown G. Beck Depression Inventory. 2nd ed. San Antonio, TX: The Psychological Corporation; 1996.
16. Carroll BJ, Feinberg M, Smouse PE, Rawson SG, Greden JF. The Carroll rating scale for depression. I. Development, reliability and validation. Br J Psychiatry. 1981;138:194-200.
17. Das AK, Olfson M, Gameroff MJ, et al. Screening for bipolar disorder in a primary care practice. JAMA. 2005;293(8):956-963.
18. Kumar G, Rissmiller DJ, Steer RA, Beck AT. Mean Beck Depression Inventory-II total scores by type of bipolar episode. Psychol Rep. 2006;98(3):836-840.
19. Feinberg M, Carroll BJ, Smouse PE, Rawson SG. The Carroll rating scale for depression. III. Comparison with other rating instruments. Br J Psychiatry. 1981;138:205-209.