Exploring new directions in statistical analysis of single-case experimental designs

We are pleased to introduce the first of two special issues dedicated to statistical andmetaanalysis of single-case experimental designs (SCEDs). This first issue is focused on the analysis of data from SCEDs while the forthcoming second issue will document the state-of-the-art in SCED research synthesis. In the field of communication disorders, SCEDs play a pivotal role for the evaluation of treatment effects. The methodology has become increasingly used in clinical research, especially when dealing with very heterogeneous populations such as, for example, autism spectrum and other developmental disorders, behavior disorders, communication disorders, learning disabilities, mental health disorders, and physical impairments. The problem of obtaining homogeneous samples of participants with similar characteristics and the high cost of clinical research make groupcomparison designs difficult to implement with these populations. Consequently, SCEDs constitute a considerable percentage of treatment studies across the fields of behavioral, disability, educational, and rehabilitation research (e.g., Schlosser, 2009; Wendt, 2007). A growing array of scholarly disciplines has incorporated SCEDs into their methodological repertoire, which is reflected by over 45 professional, peer-reviewed journals now reporting single-subject experimental research (Anderson, 2001; American Psychological Association, 2002). Despite the widespread use, SCEDs were not always recognized as a valuable source of evidence for the identification of effective clinical treatments (Evans et al., 2014). When the evidence-based practice (EBP) movement originated, the initial emphasis was on randomized-controlled trials (RCTs), and systematic reviews and metaanalyses of RCTs as preferred sources of evidence. It took certain efforts to raise the interest in and recognition of SCEDs, for example: Horner et al. (2005) pointed out the value of SCEDs in documenting EBP. Schlosser and Raghavendra (2004) explained why SCEDs should be considered Level 2 evidence alongside RCTs and quasi-experimental group designs on hierarchies of evidence for low incidence populations. Later on, the Oxford Center for Evidence-based Medicine brought attention to small sample research by classifying the randomizedN=1 trial as Level 1 evidence for deriving treatment decisions in individual patients (Howick et al., 2011). Finally, the American Speech-LanguageHearing Association (2020) included SCEDs under Experimental Study Designs suitable to answer questions about the efficacy of interventions. The increasing interest in SCEDs gained further momentum when applied research started to discuss issues of quality criteria and appraisal, as well as consistency in reporting (e.g., Kratochwill et al., 2013; Tate et al., 2014; Wendt & Miller, 2012). Similar to other areas of applied sciences, For correspondence: Oliver Wendt, School of Communication Sciences and Disorders, University of Central Florida, Orlando, FL 32816-2215. E-mail: oliver.wendt@ucf.edu Evidence-Based Communication Assessment and Intervention, 2020 Vol. 14, Nos. 1–2, 1–5, https://doi.org/10.1080/17489539.2020.1741842