Received: 26 July 2017 Accepted: 21 September 2017 DOI: 10.1002/jclp.22560 RESEARCH ARTICLE National norms for the expanded version of the inventory of depression and anxiety symptoms (IDAS-II) Graham H. Nelson 1 Michael W. O'Hara 1 David Watson 2 1 University of Iowa 2 University of Notre Dame Correspondence Graham H. Nelson, Department of Psychologi- cal and Brain Sciences, University of Iowa, E11 Seashore Hall, Iowa City, IA 52242. Email: graham-nelson@uiowa.edu Abstract Objectives The present study developed normative data for the expanded version of the Inventory of Depression and Anxiety Symp- toms (IDAS-II). The IDAS-II is a self-report measure containing 18 factor-analytically derived scales, each assessing a specific symptom of internalizing disorders, including depression, anxiety disorders, OCD, bipolar disorder, and PTSD. These normative data were used to examine group differences in internalizing symptoms across demo- graphic characteristics. Method A total of 1,836 Mechanical Turk users (47.6% male; mean age = 35.6) completed the IDAS-II; the sample was weighted to be representative of the U.S. population on gender, age, and race/ethnicity. Results Percentiles were derived for each of the IDAS-II scales. Age was the demographic characteristic most consistently associated with lower internalizing symptoms. Conclusions The present study provides information on the distri- bution of specific internalizing symptoms in a large national sam- ple, as well as on how these symptoms are related to demographic characteristics. KEYWORDS anxiety, bipolar disorder, depression, internalizing, obsessive com- pulsive disorder, posttraumatic stress disorder, test norms 1 INTRODUCTION The expanded version of the Inventory of Depression and Anxiety Symptoms (IDAS-II; Watson et al., 2012) is a 99-item measure containing multi-item scales assessing specific symptoms of internalizing disorders. Mood and anxi- ety disorders have long been recognized as sharing many similar characteristics. Increasingly, models of the structure of these disorders have recognized the need to account for the similarities among them (Brown, Chorpita, & Barlow, J. Clin. Psychol. 2018;1–16. wileyonlinelibrary.com/journal/jclp c  2018 Wiley Periodicals, Inc. 1