The Computerized Adaptive Diagnostic Test for Major Depressive Disorder (CAD-MDD): A Screening Tool for Depression

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The Computerized Adaptive Diagnostic Test for Major Depressive Disorder (CAD-MDD): A Screening Tool for Depression

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Objective: To develop a computerized adaptive diagnostic screening tool for depression that decreases patient and clinician burden and increases sensitivity and specificity for clinician-based DSM-IV diagnosis of major depressive disorder (MDD).

Method: 656 individuals with and without minor and major depression were recruited from a psychiatric clinic and a community mental health center and through public announcements (controls without depression). The focus of the study was the development of the Computerized Adaptive Diagnostic Test for Major Depressive Disorder (CAD-MDD) diagnostic screening tool based on a decision-theoretical approach (random forests and decision trees). The item bank consisted of 88 depression scale items drawn from 73 depression measures. Sensitivity and specificity for predicting clinician-based Structured Clinical Interview for DSM-IV Axis I Disorders diagnoses of MDD were the primary outcomes. Diagnostic screening accuracy was then compared to that of the Patient Health Questionnaire-9 (PHQ-9).

Results: An average of 4 items per participant was required (maximum of 6 items). Overall sensitivity and specificity were 0.95 and 0.87, respectively. For the PHQ-9, sensitivity was 0.70 and specificity was 0.91.

Conclusions: High sensitivity and reasonable specificity for a clinician-based DSM-IV diagnosis of depression can be obtained using an average of 4 adaptively administered self-report items in less than 1 minute. Relative to the currently used PHQ-9, the CAD-MDD dramatically increased sensitivity while maintaining similar specificity. As such, the CAD-MDD will identify more true positives (lower false-negative rate) than the PHQ-9 using half the number of items. Inexpensive (relative to clinical assessment), efficient, and accurate screening of depression in the settings of primary care, psychiatric epidemiology, molecular genetics, and global health are all direct applications of the current system.

J Clin Psychiatry 2013;74(7):669-674

Submitted: December 20, 2012; accepted April 5, 2013 (doi:10.4088/JCP.12m08338).

Corresponding author: Robert D. Gibbons, PhD, Center for Health Statistics, Departments of Medicine and Health Studies, University of Chicago, 5841 S Maryland Ave, MC 2007 Office W260, Chicago, IL 60637 (

With recent developments in multidimensional item response theory and computerized adaptive testing,1 the ability to undertake large-scale screening programs for the measurement of depressive severity and related mental health disorders is now possible. Large item banks consisting of hundreds of items can be constructed and adaptively administered by using a handful of items optimally targeted for each individual to produce precise measurements with small fixed levels of uncertainty. This method contrasts with the traditional approach of fixed-length tests that allow measurement uncertainty to vary from participant to participant. We have previously developed a test for depression called the Computerized Adaptive Test-Depression Inventory (CAT-DI), which requires an average of 12 items, yet maintains a correlation of 0.95 with the score from a bank of almost 400 items.1 However, in many cases, the goal of screening is to assess the likelihood of an underlying psychiatric disorder, such as major depressive disorder (MDD), rather than to obtain a dimensional measurement of the severity of that disorder. While empirically derived cut-points on an underlying continuous measure can, in certain cases, yield high sensitivity and specificity,1 this is not the direct goal of the measurement process, but rather a fortuitous by-product.

An alternative approach to traditional diagnostic assessment based on lengthy clinical interviews is computerized adaptive diagnosis (CAD), in which individuals answer a series of symptom questions until there is high probability that they either do or do not have the diagnosis (eg, MDD) in question. To produce such a diagnostic screening system requires a large item bank that has been administered to large groups of participants who do and do not meet criteria for the disorder on the basis of an assessment for the disorder using trained clinical interviewers following an established diagnostic system. These data are then used to calibrate the CAD system such that the probability of having the diagnosis can be assessed on the basis of any pattern of responses to the set of administered items for that particular individual. The adaptive part of the algorithm selects the next most informative item to administer on the basis of the responses to the items that have been previously administered. Unlike computerized adaptive testing (CAT), which is based on item response theory (IRT) in which the goal is to estimate the underlying severity of the disorder with a fixed level of uncertainty, the goal of CAD is to estimate the likelihood that a clinical interview would have obtained a positive or negative diagnosis with a specified level of confidence. While CAT is based on IRT, CAD is based on decision-theoretical models such as decision trees and random forests,2 and while the goal of CAT is to administer items at the point of maximum information regarding a person’s estimated level of impairment, the goal of CAD is to administer items at the point at which the probability shifts from a negative to a positive diagnosis.

Although CAT and CAD are based on very different underlying statistical ideas, with very different goals, they are in fact complementary. For example, in screening patients for depression in primary care, we may initially screen patients for the presence or absence of MDD using CAD and then monitor their response to treatment in terms of changes in their depressive severity using CAT. The purpose of this article is to illustrate the use of CAD for MDD using a large item bank drawn from the DSM-IV depression diagnostic system in a sample of individuals seeking treatment for depression (some of whom did and some of whom did not meet DSM-IV criteria for MDD) and nonpsychiatric controls.

In this context, it is important to draw distinctions between diagnosis, screening, and case finding. Screening is used in a population to identify an unrecognized disease in individuals for whom the symptoms of the disease have not yet led to its recognition. Case finding involves identification of risk factors (eg, family history) that increase the likelihood of identifying the disease, typically in a much smaller sample from the population, often for the purpose of conducting a scientific study in patients who have the disease of interest. The Computerized Adaptive Diagnostic Test for Major Depressive Disorder (CAD-MDD) is a screening measure, not a case-finding measure. Screening measures, like the CAD-MDD, are not diagnostic measures because they do not estimate the potential for the disease; rather, they confirm the presence or absence of the disease in symptomatic individuals. Typically, screening instruments are brief and noninvasive and are chosen to maximize sensitivity. Conversely, diagnostic tests are always more invasive and more costly in terms of time or financial commitments and focus on high specificity to rule out true negatives.

clinical points

  • The Computerized Adaptive Diagnostic Test for Major Depressive Disorder (CAD-MDD) permits highly accurate screening for depression in less than 1 minute anywhere and anytime via any Internet-capable device.
  • This tool can be used to screen primary care patients for depression.
  • The CAD-MDD provides similar specificity but higher sensitivity than the Patient Health Questionnaire-9 using half the number of items.


Statistical Methods

Our methods are based on representing the classification of study participants as a decision tree. Decision trees3,4 represent a model in terms of a flowchart (Figure 1). Decisions are made by traversing the tree starting from the top node. At each node in the tree, a participant is asked to respond to a particular item (denoted by "Qxxxx" in Figure 1). The participant progresses down the tree to the node to the left if his or her response is less than the cutoff value for the node and to the right otherwise (denoted by the inequality operators and numbers in Figure 1). The bottom node of the tree reports a classification for the participant (0 = non-MDD and 2 = MDD in Figure 1, with the value 1 reserved for minor depression and dysthymia). Decision trees are appealing in this context because they allow the set of items presented to adapt to the responses already provided—going left at a node may result in a very different set of items being presented as compared to going right. This feature has the potential to considerably shorten the length of the instrument.

Figure 1

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Despite their appeal, decision trees have frequently suffered from poor performance.5 This is because algorithms used to build trees from data can exhibit sensitivity to small changes in the data sets that are provided. Instead, ensemble models constructed of averages of hundreds of decision trees have received considerable attention in statistics and machine learning.2,6-8 These models provide significant improvements in predictive performance as compared to individual trees. However, averaging hundreds of trees destroys the adaptive testing structure that makes them appealing for the purposes of medical questionnaires.

To obtain both the advantages of individual trees and the accuracy of ensemble models, we used a combined approach. We first fit a type of ensemble model known as a random forest2 to the data. Random forests were chosen because they require minimal human intervention and have historically exhibited good performance across a wide range of domains.2,5 We then generated a very large artificial data set in which the items mimicked the distribution of the items in the original data set. A single tree was then estimated on this artificial data set with the intention of mimicking the output of the random forest as closely as possible while using enough data to reduce the sensitivity of the tree to small perturbations.

In our implementation, all estimation was performed in the R statistical programming language Random Forest9 to estimate the random forest and r part to estimate the final decision tree. Trees of depth 6 and 11 items each were used in the analysis. Cross-validation was performed by dividing the data into 10 subgroups, and for each subgroup we used 9 groups to build the model and then performed testing on the 10th group.

We studied the ability of the CAD-MDD to reproduce clinician-based Structured Clinical Interview for DSM-IV Axis I Mood Disorders (SCID) diagnoses of MDD using sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV). PPV is the proportion of people who screen positive for MDD that have a confirmed DSM diagnosis of MDD and is therefore a good case-finding measure. NPV is the proportion of people who screen negative for MDD that do not have MDD on the basis of a complete diagnostic interview and is therefore a good screening measure. Tests with low false-positive rates will have high PPV, and tests with low false-negative rates will have high NPV.

Study Population

Psychiatric participants for this study were male and female treatment-seeking outpatients (n = 259) and nonpsychiatric controls (n = 397) between 18 and 80 years of age. Patients were recruited from 2 facilities, the Bellefield Clinic at the University of Pittsburgh (Western Psychiatric Institute and Clinic [WPIC]; Pittsburgh, Pennsylvania) and a community clinic at DuBois Regional Medical Center (DuBois, Pennsylvania) that provides comprehensive inpatient and outpatient psychiatric care. Patient participants were recruited through advertisements, the WPIC outpatient clinics, and clinician referrals and screened at both WPIC and DuBois for eligibility as described below. Nonpsychiatric controls were recruited through advertisements (eg, flyers) and were screened by a trained clinical interviewer to ensure that they had not been in treatment for the past 2 years, which was also corroborated by medical records. All clinic and community clinic patients received a full SCID diagnostic interview. No one refused to use the computer, as this was described as part of the study before enrollment. Any participant with computer or language issues was given assistance.

Exclusion criteria for psychiatric participants were as follows: history of schizophrenia, schizoaffective disorder, or psychosis; organic neuropsychiatric syndromes (eg, Alzheimer’s disease or other forms of dementia, Parkinson’s disease); drug or alcohol dependence within the past 3 months (however, patients with episodic abuse related to mood episodes were not excluded); inpatient treatment status; and inability or unwillingness to provide informed consent. Exclusion criteria for nonpsychiatric controls were as follows: any psychiatric diagnosis within the past 24 months; treatment for a psychiatric problem within the past 24 months; positive responses to phone screen questions regarding depressive symptoms; history of schizophrenia, schizoaffective disorder, or psychosis; and inability or unwillingness to provide informed consent.

Demographic information is displayed in Table 1. Race includes multiple races per individual when appropriate, so the percentages sum to a value greater than 100%. If it was determined during the diagnostic interview that a participant was not eligible (because of a bipolar, psychosis, or substance abuse diagnosis), the individual was excluded from the study. This was not typical, but did happen, usually because the potential participant either lied during screening or did not know their diagnosis (ie, said they were treated for depression, but were actually treated for bipolar disorder and were currently in a depressed episode). All eligible participants completed the study.

Table 1

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Item Bank

Eighty-eight depression scale items were identified as aligned with current DSM-IV MDD diagnosis on the basis of content review by expert judges. The items were chosen from an extensive literature search in the MEDLINE, PsycINFO, and HAPI databases. They were based on 73 frequently used depression measures (eg, Center for Epidemiologic Studies Depression Scale, Beck Depression Inventory, Mood and Anxiety Symptom Questionnaire, Inventory of Depressive Symptomatology, Crown-Crisp Experiential Index, and Minnesota Multiphasic Personality Inventory) and a total of 501 depression items. Items selected for inclusion into this item bank were those that are aligned with the following 9 DSM-IV criteria for MDD diagnosis: depressed mood, loss of interest or pleasure in activities, loss or gain of weight, insomnia or hypersomnia, agitation or slowed behavior, fatigue, thoughts of worthlessness or guilt, inability to think or concentrate, and suicidality. Final items selected were all in the public domain. Participants were also administered the Patient Health Questionnaire-9 (PHQ-9)10 via paper and pencil. For comparison purposes, we followed PHQ guidelines for making a tentative depression diagnosis as (1) endorsed ≥ 5 symptoms as at least "more than half the days" on questions Q1 -Q8 or the symptom in Q9 (suicide question) if it is present at all; (2) endorsed questions Q1 or Q2 as at least "more than half the days"; and (3) endorsed functional impairment, Q10 score > 1. We also considered the PHQ-2 depressive diagnostic screen of a score of 3 or more on the first 2 items of the PHQ-9 and the PHQ-9 depressive diagnostic screen of a score of 10 or more on all 9 items.


The diagnosis of MDD was made by a trained clinical interviewer using the SCID.11 As depression represents a continuum from mild symptoms to intermediate states like partial remission to major depression, we wanted to choose a diagnostic interview that would allow for such specificity in diagnoses. The SCID also allowed us to rule out other Axis I disorders such as anxiety disorders. Five interviewers were used during the course of the study. All had master’s -level training in psychology, counseling, or social work and job experience in mental health settings. Interviewers were trained using a library of videotaped SCID interviews. Training and discussion focused on developing common rating conventions, including a shared understanding of thresholds for severity to be used on each of the SCID items.12 Five additional interviews were reviewed by the team throughout the duration of the project to avoid rater drift.12 Interrater reliability of the SCID MDD diagnoses was determined for 5 raters based on 13 subjects. The agreement was excellent (κ = 0.92, SE = 0.10, P < .001).

The CAT-MDD received expedited approval from the University of Pittsburgh Institutional Review Board on a yearly basis, with no adverse events or ethical issues reported.


A total of 656 participants were screened; 134 participants met criteria for MDD, 27 met criteria for minor depression, and 495 met criteria for neither major nor minor depression. Results were similar for trees of 6 and 11 nodes; therefore, the 6-node tree was selected as the most parsimonious choice. An average of 4.2 items per participant (maximum = 6) was administered. The overall sensitivity and specificity for MDD were 0.95 and 0.87, respectively. Following cross-validation, results were similar (sensitivity = 0.94 and specificity = 0.82). Figure 2 displays the entire cross-validated receiver operating characteristic curve, showing the balance between sensitivity (true positives) and 1 specificity (false positives) throughout the decision space. By comparison, the PHQ-9 MDD diagnostic screen provided sensitivity of 0.70 and specificity of 0.91, the PHQ-9 screen for both other depressive disorder and MDD provided sensitivity of 0.83 and specificity of 0.82, the PHQ-2 provided sensitivity of 0.86 and specificity of 0.86, and the simple PHQ-9 screen (total score of 10 or more) provided sensitivity of 0.85 and specificity of 0.79.

Figure 2

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For the CAD-MDD, PPV was 0.66 (95% CI, 0.62-0.68), and NPV was 0.98 (95% CI, 0.97-0.99). For the PHQ-9, PPV was 0.81 (95% CI, 0.72-0.88), and NPV was 0.84 (95% CI, 0.80-0.88).

Among the 27 participants with minor depressive disorder, 20 (74%) were classified as having a depressive disorder, whereas the other 7 (26%) were classified as nondepressed cases. This finding reveals that roughly three-quarters of patients with minor depression or dysthymia will be identified via this screening tool.

To illustrate the methodology, Table 2 shows 2 sample testing sessions and the administered questions and responses for a low-severity patient without MDD and a high-severity patient with MDD. The resulting MDD diagnoses were negative for the first patient, with confidence of 96.4%, and positive for the second patient, with confidence of 99.3%. Overall, the mean assessment time was 46 seconds (standard deviation = 29 seconds). Faster times are likely using a touch-screen interface, as illustrated in Table 2 by the testing times of 36 and 35 seconds with this interface.

In terms of participant satisfaction, 94.4% gave a positive overall rating of the computer questionnaire, and 91.0% said they would prefer to answer these questions on a computer. Further, 97.3% of participants stated that they tried to answer honestly and accurately, with the remainder answering "neutral." In response to the question, "How much did the questions describe your experience with mood problems?" 30.8% answered "a great deal," 38.2% answered "very much," and 24.6% answered "somewhat."

Table 2

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Results of this study reveal that we can achieve high sensitivity and reasonable specificity for a clinician-based DSM-IV diagnosis of depression using an average of 4 self-report items. The entire diagnostic screening test requires less than a minute and can be administered via a cloud-computing environment over the Internet to smartphones, tablets, notebooks, and personal computers. Cross-validated sensitivity of 0.94 indicates that we will rarely miss a validated case of current depressive disorder, and the cross-validated specificity of 0.82 indicates that approximately 18% of patients who did not meet criteria for MDD would be identified as having a possible depressive disorder and would require further evaluation and/or treatment. Results for the PHQ were more varied. The PHQ-9 depression diagnostic screen algorithm had a high specificity of 0.91 (ie, low false-positive rate) but a poor sensitivity of 0.70 (high false-negative rate). The simple PHQ-2 appeared to provide a better balance, with sensitivity and specificity of 0.86 (from 0.70 and 0.91), and the simple PHQ-9 threshold of 10 or more increased sensitivity to 0.85 (from 0.70), at the cost of decreasing specificity to 0.79 (from 0.91). Compared with all of the PHQ scoring methods, the CAD-MDD produced considerably higher sensitivity with comparable specificity.

The PPV and NPV estimates point out important differences between the CAD-MDD and PHQ-9 and their utility for diagnostic screening. The exceptionally high NPV indicates that it is extremely rare that the CAD-MDD will miss a real case, which is consistent with the high sensitivity of the CAD-MDD. The lower NPV for the PHQ-9 is consistent with the lower sensitivity and indicates that a fair number of true cases will be screened negative. By contrast, the PHQ-9 has higher PPV and specificity, indicating that when it is positive, there is high probability that it has identified a true case. As previously noted, this makes the PHQ-9 better for case finding than diagnostic screening; however, this is not the real objective of either test. It should be noted that PPV and NPV are highly dependent on prevalence. The prevalence in our study may not be representative of the prevalence of MDD in the general population, making these measures of validity less useful.

We have evaluated the CAD-MDD in psychiatric settings to ensure that we have a large number of true cases so that we can obtain a function that maximally differentiates cases from controls. We have also included a large number of nonpsychiatric controls to insure that the CAD-MDD will work well in both mental health and non-mental health settings. Ultimately, the use of the CAD-MDD will be in settings such as primary care where treatment is not necessarily for a psychiatric indication and its role as an effective screener can be the primary focus. In psychiatric populations, the CAT-DI would usually be used to monitor the effectiveness of treatment in patients presenting with a psychiatric illness.

Traditional fixed-length short-form tests such as the PHQ-9 have been used for the purposes of both diagnostic screening and measurement of severity. At first, this may seem advantageous, but it is not. The measurement of severity should focus on maximizing information at the true level of severity of the individual. By contrast, a screening measure should focus on maximizing information at the point at which the diagnosis shifts from negative to positive. These are 2 very different types of measurement problems that lead to very different statistical foundations. Developing different instruments for screening (eg, the CAD-MDD) and measurement (the CAT-DI) increases both accuracy and precision and minimizes burden because those patients screening positive will have taken an average of only 4 items rather than an average of 12 items used to measure severity.

There are several limitations of this study. The study sample was largely a psychiatric sample, and it is unclear what the sensitivity and specificity of the CAD-MDD are in a primary care setting or medical inpatient setting. While the overall rate of MDD in the full sample of patients and controls based on the SCID was 20.4%, among the psychiatric patient sample, the rate was 51.7%, which is considerably higher than would be observed in general medical settings. The decision trees were based on an adult sample from the Pittsburgh area, and as a consequence may not directly apply to the assessment of depression in children, the elderly, or cultural groups such as Latinos not represented in the Pittsburgh area. Further study of the generalizability of our results to these populations is required. While sensitivity of the CAD-MDD is extremely high, specificity is more modest. This may, in fact, be an advantage for large-scale screening whereby patients who do not meet DSM criteria for MDD may still have significant psychopathology and deserve further assessment. Finally, we excluded subjects with current substance abuse. Further study of the generalizability of our results to patients with substance abuse would be of considerable interest.

Recent developments in the IRT/CAT literature in the area of diagnostic classification are also starting to emerge.13,14 The principal difference between the CAD-MDD and diagnostic classification CAT is that the former requires an external criterion such as a clinician-based diagnosis and the latter involves a latent classification.14 The basic idea is to adapt CAT to an underlying latent class model for an underlying binary classification instead of the traditional use of CAT for a continuous latent variable based on IRT. Although beyond the scope of this article, it would be quite interesting to compare the results of the current approach in which an external criterion is used to the alternative criterion-free approach based on an underlying latent class model.

Not surprisingly, the results of our study revealed that the CAD-MDD is even more sensitive and specific for diagnostic screening than the CAT-DI, which was developed to provide a dimensional severity measure of depression. What is surprising is that it can achieve these levels of sensitivity and specificity using an average of only 4 items. We now have the ability to efficiently screen large populations for MDD. Additional potential applications include depression screening in primary care, assessment of mental health phenotypes for genetic studies, and large-scale psychiatric epidemiologic studies.

Author affiliations: Center for Health Statistics, University of Chicago, Chicago, Illinois (Dr Gibbons); Department of Statistics, Cornell University, Ithaca, New York (Dr Hooker); Department of Public Health and Community Service, Tufts University School of Dental Medicine, Boston, Massachusetts (Dr Finkelman); Department of Psychology, University of Minnesota, Minneapolis (Dr Weiss); and Western Psychiatric Institute, University of Pittsburgh, Pittsburgh, Pennsylvania (Drs Pilkonis, Frank, and Kupfer and Ms Moore).

Potential conflicts of interest: The CAD-MDD will be made available for routine administration (by the end of 2013) through Adaptive Testing Technologies (, in which Drs Gibbons, Weiss, Pilkonis, Frank, and Kupfer have financial interests. Dr Frank has been a member of advisory boards for and received honoraria from Servier and receives royalties from Guilford Press and American Psychological Association Press. Dr Kupfer is a consultant for the American Psychiatric Association. Drs Hooker and Finkelman and Ms Moore report no potential conflict of interest.

Funding/support: This work was supported by National Institute of Mental Health grant R01-MH66302.

Acknowledgments: The authors acknowledge the outstanding support of R. Darrell Bock, PhD, University of Chicago (technical comments on methodology); Scott Turkin, MD, DuBois Community Mental Health Center (data collection); Damara Walters, MA, University of Pittsburgh (patient recruitment); Suzanne Lawrence, MA, University of Pittsburgh (diagnostic assessments); and Victoria Grochocinski, PhD, University of Pittsburgh (database administration). Dr Turkin has been a speaker for Forest and Sunovion. Drs Bock and Grochocinski and Mss Walters and Lawrence report no conflict of interest. The authors are also indebted to the reviewers for many excellent comments and suggestions.


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