Journal of Behavior Therapy and Experimental Psychiatry 70 (2021) 101609 Available online 8 September 2020 0005-7916/© 2020 Elsevier Ltd. All rights reserved. Feasibility and effcacy of a digital CBT intervention for symptoms of Generalized Anxiety Disorder: A randomized multiple-baseline study ☆ Christopher B. Miller a, b, c, * , Jenny Gu a, b, d , Alasdair L. Henry a, b, c , Michelle L. Davis a, b , Colin A. Espie a, b, c , Richard Stott a, b, d , Adrienne J. Heinz a, b , Kate H. Bentley f , Guy M. Goodwin d , Bernard S. Gorman e , Michelle G. Craske g , Jenna R. Carl a, b a Big Health Inc., San Francisco, CA, USA b Big Health Inc., London, UK c Sleep and Circadian Neuroscience Institute, Nuffeld Department of Clinical Neurosciences, Sir William Dunn School of Pathology, University of Oxford, Oxford, UK d University Department of Psychiatry, University of Oxford and Oxford Health NHS Trust, Warneford Hospital, Oxford, UK e Department of Psychology, Harvard University, Cambridge, MA, USA f Derner School of Psychology, Adelphi University, Garden City, NY, USA g Anxiety and Depression Research Centre (ADRC), UCLA, Los Angeles, CA, USA A R T I C L E INFO Keywords: Anxiety Digital Cognitive behavioral therapy Single-case experimental design Smartphone ABSTRACT Background and objectives: Cognitive behavioral therapy (CBT) is a frst-line treatment for anxiety, but it is not widely available as clinical guidelines recommend. We examined the feasibility and effcacy of a novel smartphone-based fully automated digital CBT intervention, ‘Daylight™‘, to improve symptoms of Generalized Anxiety Disorder (GAD). Methods: In this multiple-baseline design, 21 adults (20 F; mean age 43yrs. range 19–65yrs.) with moderate-to- severe symptoms of GAD were randomized to one of three baseline durations (2-, 4-, or 6-weeks) and then received access to digital CBT. Participants completed daily ratings of anxiety and worry, weekly measures of anxiety, depressive symptoms, and sleep, and measures of anxiety, worry, wellbeing, quality of life, CBT skill acquisition, and work performance at initial assessment prior to baseline randomization, post-intervention, and follow-up. Results: Digital CBT was found to be feasible in terms of engagement, satisfaction, and safety. For preliminary effcacy, improvements were detected in daily and weekly outcomes of anxiety for most participants. Despite individual differences, signifcant improvements occurred with the introduction of digital CBT and not during baseline. Overall, 70% of participants no longer had clinically signifcant symptoms of GAD, 61% no longer had signifcant depressive symptoms, and 40% no longer had signifcant sleep diffculty at post-intervention. Limitations: The study sample was recruited using the internet and was mostly female, limiting the generaliz- ability of the fndings. Conclusions: Findings support the feasibility and effcacy of Daylight. Further examination in randomized controlled trials is now warranted. 1. Introduction Generalized Anxiety Disorder (GAD) is characterized by symptoms of excessive worry and anxiety that are diffcult to control (American Psychiatric Association, 2013). Approximately 5–8% of adults are affected by GAD (Kessler et al., 2005; Kroenke, Spitzer, Williams, Monahan, & L¨ owe, 2007; Roy-Byrne & Wagner, 2004), effects of which include impaired health status, wellbeing, life satisfaction, increased healthcare utilization, and decreased work productivity (Loebach Wetherell et al., 2004; Stein & Heimberg, 2004; Wittchen, 2002). Both Cognitive Behavioral Therapy (CBT) and pharmacotherapy are frst-line interventions for GAD (Anxiety and Depression Association of America, 2020; Canadian Psychiatric Association, 2006; Locke, Kirst, & Shultz, 2015; National Institute for Health and Clinical Excellence, ☆ Clinical Trial Registry Number: ISRCTN89276818 (http://www.isrctn.com/ISRCTN89276818). * Corresponding author. Big Health, Runway East London Bridge, 20 St. Thomas St., London SE1 9RS, UK. E-mail address: chris.miller@bighealth.com (C.B. Miller). Contents lists available at ScienceDirect Journal of Behavior Therapy and Experimental Psychiatry journal homepage: www.elsevier.com/locate/jbtep https://doi.org/10.1016/j.jbtep.2020.101609 Received 23 December 2019; Received in revised form 10 July 2020; Accepted 17 August 2020