The Hidden Psychometric Model Underlying the DSM: What Happens When It Fails to Fit Psychiatric Data.

Back to table of contents Next article DatapointsFull AccessThe Hidden Psychometric Model Underlying the DSM: What Happens When It Fails to Fit Psychiatric DataAntonio A. Morgan-López, Ph.D., Lissette M. Saavedra, Ph.D., Krithika Prakash, M.S., Stephen G. West, Ph.D., Denise A. Hien, Ph.D.Antonio A. Morgan-López, Ph.D., Lissette M. Saavedra, Ph.D., Krithika Prakash, M.S., Stephen G. West, Ph.D., Denise A. Hien, Ph.D.Published Online:21 May 2024https://doi.org/10.1176/appi.ps.20230370AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail Diagnostic criteria for a DSM psychiatric diagnosis are typically met by within-criterion symptom counts. Simple symptom counts treat each symptom as though it has equal priority (or "weight") in reflecting underlying disorder severity. In clinical practice, many practitioners understand that "some symptoms matter more than others" (1). Two patients who have the same number of symptoms, but a different pattern of those symptoms, will likely have different underlying disorder severities (2). Thus, a simple total count of symptoms can give a distorted picture of a patient's disorder severity and changes in severity following treatment (2, 3).Factor analysis (FA) and item response theory (IRT) methods incorporate differences in the clinical weights of symptoms in relation to underlying disorder severity (2). Severity scores are weighted by factor loadings in FA or equivalently by discrimination parameters in IRT. In contrast, symptom counting assumes equal weights, which often fail to fit psychiatric symptom data when these data are formally tested (2, 3). FA- and IRT-based scores may be highly correlated with symptom counts (r>0.90). However, as Figure 1 shows, high correlations between these scores do not represent equivalence (2).FIGURE 1. Scatterplot of posttraumatic stress disorder (PTSD) symptom counts and IRT severity scoresaaIRT, item response theory.Figure 1 presents data reported by Morgan-López et al. (4) that were collected with the Clinician-Administered PTSD Scale for DSM-IV (CAPS-IV). Patients (N=353) were grouped by CAPS-IV diagnosis (full or subthreshold posttraumatic stress disorder [PTSD]) and by an empirical diagnosis based on the weighted midpoint of the IRT score distributions between the full and subthreshold diagnostic groups. The correlation between symptom counts and IRT scores was 0.95; high correlations between symptom counts and FA- or IRT-based scores are often cited as justification for using symptom counts (2). However, patients with the same number of symptoms (y-axis) can vary appreciably (i.e., by >1 standard deviation in each horizontal band of data) in underlying PTSD severity (x-axis) because the combination of symptoms varies (2, 3).Equal weighting of symptoms in the DSM contrasts with weighting methods that assume variability in the importance of symptoms. However, cross-population measurement studies are necessary for assessing whether the relative weights of each PTSD symptom can be universally applied; the weights of some symptoms are expected to vary in certain populations (5). Given the importance of precise measurement of underlying psychiatric severity and classification, patients would benefit from greater use of symptom-weighting approaches for DSM-based psychiatric assessments and a potential path forward for including symptom weighting in clinical practice.RTI International, Research Triangle Park, North Carolina (Morgan-López, Saavedra); Department of Psychology, Eastern Michigan University, Ypsilanti (Prakash); Department of Psychology, Arizona State University, Tempe, and Methods and Evaluation Division, Freie Universität Berlin, Berlin (West); Center of Alcohol and Substance Use Studies, Rutgers University, Piscataway, New Jersey (Hien).Send correspondence to Dr. Morgan-López ([email protected]). Tami L. Mark, Ph.D., and Alexander J. Cowell, Ph.D., are editors of this column.Supported by National Institute on Alcohol Abuse and Alcoholism grants R01 AA025853 (to Drs. Morgan-López and Hien), R25 AA028464, and R01 MH124438 (to Dr. Morgan-López) as well as by the National Institute on Drug Abuse's Clinical Trials Network protocol 0015 (to Dr. Hien).The authors report no financial relationships with commercial interests.The funders had no role in the preparation, review, or approval of the manuscript or in the decision to submit the manuscript for publication. The views presented in this column do not necessarily represent those of the NIH or the U.S. government.References1. Galatzer-Levy IR, Bryant RA: 636,120 ways to have posttraumatic stress disorder. Perspect Psychol Sci 2013; 8:651–662Crossref, Medline, Google Scholar2. McNeish D: Psychometric properties of sum scores and factor scores differ even when their correlation is 0.98: a response to Widaman and Revelle. Behav Res Methods 2023; 55:4269–4290Crossref, Medline, Google Scholar3. Morgan-López AA, Hien DA, Saraiya TC, et al.: Estimating posttraumatic stress disorder severity in the presence of differential item functioning across populations, comorbidities, and interview measures: introduction to Project Harmony. J Trauma Stress 2022; 35:926–940Crossref, Medline, Google Scholar4. Morgan-López AA, Killeen TK, Saavedra LM, et al.: Crossover between diagnostic and empirical categorizations of full and subthreshold PTSD. J Affect Disord 2020; 274:832–840Crossref, Medline, Google Scholar5. Morgan-López AA, Saavedra LM, Hien DA, et al.: Differential symptom weighting in estimating empirical thresholds for underlying PTSD severity: toward a "platinum" standard for diagnosis? Int J Methods Psychiatr Res 2023; 32:e1963Crossref, Medline, Google Scholar FiguresReferencesCited byDetailsCited byNone Metrics Keywordsdiagnosis/classification (DSM)assessment/psychiatricpsychological testsresearch design and methodologyscales/outcome and clinical measurementPDF download History Received 26 July 2023 Revised 22 November 2023 Accepted 13 March 2024 Published online 21 May 2024