Quality of Single-Case Designs Targeting Adults’ Exercise and Physical Activity

Exercise and physical activity (ExPA) interventions require substantial preefficacy and efficacy testing before dissemination at the clinical and community level. Single-case designs (SCD; i.e., small-scale experiments where participants serve as their own controls) hold promise for preefficacy intervention development and refinement. At present, SCD may be underutilized in ExPA promotion, potentially because of the perceived lack of methodological rigor. Purpose: This review aimed to evaluate the quality of SCD research used to test ExPA promotion strategies in adults. Methods: Combinations of key words related to SCD and ExPA were used to search PubMed, Web of Science, and PsycINFO between July and October 2017. Of the 120 individual searches, 1227 titles were found, 10 of which met inclusion criteria. Two published quality assessment tools were then used to analyze SCD quality. Results: Average quality scores were 10 out of 14 (range 8–12) for the first tool and 13 out of 15 (range 9–15) for the second tool. Commonly unmet criteria included the use of assessor blinding (unfulfilled by 100% of studies), fidelity reporting (unfulfilled by 100%), inter-/intrarater reliability (unfulfilled by 80%), and appropriate statistical analyses (unfulfilled by 60%). Conclusion: Quality scores of SCD reporting were moderate to strong, but commonly missed criteria represent rigorous reporting standards for behavioral science. Although not specifically addressed in the quality assessment tools, it is important to note that only one study reported the ExPA prescription with replicable precision (i.e., specific reporting of exercise frequency, intensity, time, type, volume, and progression). Researchers should strive to meet all criteria and provide transparency to elevate the use of SCD for ExPA intervention development before effectiveness testing in real-world conditions. INTRODUCTION Physical inactivity in adults, a leading contributor to multiple noncommunicable diseases (e.g., metabolic disorders, certain cancers, cardiovascular disease), increases risk of premature mortality in the United States (1). Physical activity is Department of Kinesiology, Recreation, and Sport Studies, The University of Tennessee, Knoxville, Knoxville, TN Address for correspondence: Paula-Marie M. Ferrara, M.S., ACSM-CEP, Health, Physical Education, and Recreation Building, The University of Tennessee, Knoxville, 1914 Andy Holt Ave., Knoxville, TN 37996 (E-mail: pferrar1@vols.utk.edu). 2379-2868/0423/0257–0265 Translational Journal of the ACSM Copyright © 2019 by the American College of Sports Medicine http://www.acsm-tj.org Copyright © 2019 by the American College of Sports Medicine. Unauthorized repro defined as any bodily movement produced by skeletal muscle that increases energy expenditure above rest, whereas exercise (a subset of physical activity) refers to structured, repetitive activity conducted with the goal of improving one or more components of physical fitness (2). Evidence-based guidelines promoted by the American College of Sports Medicine and the United States Office of Disease Prevention and Health Promotion state adults should obtain the metabolic equivalent of 150 min of moderate-intensity aerobic exercise and physical activity (ExPA) and engage in resistance exercises of all major muscle groups two or more times, per week (3,4). Although easy to interpret, these guidelines do not explicitly state how to reach or maintain these goals once achieved. Presently, only 20% of American adults meet both aerobic and strengthening recommendations (5), with different factors cited preventing them from regularly engaging in ExPA, including internal barriers (e.g., lack of motivation, boredom, and time constraints) and environmental barriers (e.g., weather conditions and lack of exercise equipment), lack of support from family or friends, and physical or health limitations (6). Researchers have used different methods to improve ExPA levels in inactive populations, including educating individuals on practices and benefits (7,8), incorporating material/monetary incentives (9,10), and applying cognitive behavioral strategies (8,11). However, although various types of behavioral interventions are often successful in initiating ExPA adoption, poor long-term adherence poses a major concern (12,13). To date, behavior researchers rely heavily on randomized controlled trials (RCT) for intervention development, as this method represents the gold standard in testing causal relationships (14,15). However, the relatively slow pace and high cost of conducting RCT may place substantial barriers in translating research from basic biological/psychological testing to real-world practice (16). Further, RCToutcomes tend to focus Translational Journal of the ACSM 257 duction of this article is prohibited. on differences between group means, limiting researchers’ understanding of potentially important factors between and within participants’ responses to treatment (16,17). These limitations sometimes cause promising behavioral treatments to be abandoned, rather than refined, if they do not achieve statistically significant outcomes early on in their development (18). In addition, treatments not tested rigorously in preefficacy and efficacy trials can ultimately fail if prematurely translated to patient and community populations. Different frameworks, such as the Medical Research Counsel guidelines for developing and evaluating complex interventions (19) and the Obesity-Related Behavioral Interventions Trials model (18), have been established to guide researchers in rigorously testing aspects of health-related interventions early on in development before dissemination at the clinical and community level. These frameworks provide a basis for the intervention refinement process; they are general, making them adaptable to a wide variety of health and behaviorrelated interventions, but do not provide specific methods to use in the various stages of refinement, leaving much up to interpretation by researchers. There is a critical need for researchers to develop, test, and refine behavioral interventions in preefficacy stages using methods that are efficient and rigorous but also flexible (12). In doing so, more successful, efficacious health-based interventions may be translated to the general population. The purpose of preefficacy designs is to test and define appropriate intervention components based on preliminary measurements of causation. Different types of preefficacy designs exist, each with its own goals and standards to meet. For example, experimental and observational studies in a laboratory setting or in the field enable researchers to identify and define potential treatment components necessary to affect behavior (18). Quasi-experimental studies, where participants act as their own control and pre-/postmeasurement means are analyzed, help researchers determine proof of concept and whether a design warrants more rigorous testing (18). Pilot studies allow the protocol to be implemented at a small scale (e.g., one person or group) and allow researchers to ascertain whether clinically significant outcomes can be replicated in a larger sample (18). Feasibility testing lets researchers assess the practicality of design protocols and provides estimates for future efficacy trials (18). These designs can be built on one another to define and refine intervention components to be tested in future randomized trials (18,19). Although the use of these various preefficacy designs is common in ExPA research, experts behind the Medical Research Counsel and the Obesity-Related Behavioral Interventions Trials model, as well as several behavioral researchers, endorse the increased use of single-case designs (SCD) in preefficacy stages of intervention development (12,18–20). Although the terminology for SCD can vary (e.g., single-case experimental design, small-case design, and single-subject design), the primary purpose of these designs is to make causal inferences using relatively small sample sizes (~6–20 participants or cases). Multiple SCD approaches exist that use the methods of delayed-treatment onset (multiple baseline design), treatment reversal (ABAB design), treatment progression (changing criterion design), or combined methodologies in the intervention (12). Because of the small sample sizes, each of these different methods relies on participants serving as their 258 Volume 4 • Number 23 • December 1 2019 Copyright © 2019 by the American College of Sports Medicin own controls to enhance internal validity (12). Further, because they are underpowered for traditional parametric statistics, researchers use visual analysis to assess clinical relevance regarding primary outcomes. A unique characteristic of SCD, unlike traditional pre-/postdesigns, is the requirement ofmultiple measurements taken within baseline and intervention phases. This intensive assessment of participants’ behavior over time accommodates the internal “idiosyncratic and dynamic” behavioral changes individuals inevitably experience within the intervention (12). More in-depth data per participant can yield useful insight into inter-/intraindividual responses to treatment in preefficacy stages of intervention design (12). For these reasons, SCD could be an insightful and cost-effective approach to be used in early stages of intervention development before translation to larger preefficacy designs (e.g., quasi-experimental studies, pilot studies) and eventual randomized trials. Unfortunately, SCD methodologies appear to be relatively underutilized in ExPA research (20), potentially because of the lack of awareness or misconceptions about perceived lack of rigor in these designs among those trained in conventional RCT methodology (21,22). In a previous systematic review, Gorczynski (20) examined available ExPA research literature to identify studies that used SCD methodology. Ten studies were summar