EVALUATION & THE HEALTH PROFESSIONS

The Dual Effect of Work Rumination in the Relationship Between Challenge Stress and Innovative Behavior: A Moderated Mediation Model of Information Literacy
Yao L, Li S, Yao L, Fang Y, Gao C, Chai Y, Yi X, Jia Q and Dai J
Innovation in healthcare is crucial for enhancing patient care and operational efficiency. Nurses often experience stress that may impede the process of innovation. This study utilizes the Job Demands-Resources model and Cognitive Appraisal Theory to investigate the impact of challenge stress, work rumination, and information literacy on the expression of innovative behaviors among nurses. A cross-sectional survey was conducted in China in June 2024, involving a sample of 533 nurses. Participants were required to complete online questionnaires designed to evaluate challenge stress, work rumination, information literacy, and innovative behavior. The data collected were analyzed using the PROCESS macro in SPSS. Challenge stress exhibited a statistically significant positive correlation with innovative behavior (r = 0.142, < .01) and work rumination (r = 0.348, < .01). The relationship between challenge stress and innovative behaviors was partially mediated by work rumination. Affective rumination was found to exert a negative influence, while problem-solving pondering demonstrated a positive impact. The relationship between work rumination and innovative behaviors was moderated by information literacy (β = 0.069, = .019), indicating that the effects were more pronounced at higher levels of information literacy among nurses. Challenge stress enhances innovative behaviors through work rumination. The presence of information literacy further amplifies these positive effects, particularly via problem-solving pondering. However, it is important to note that affective rumination impede this process.
Commentary: Review of Mandatory Maintenance of Certification in the USA
Peri K and Eisenberg MJ
The goal of maintenance of certification (MOC) activities is to ensure physicians are up to date on current practices and demonstrate the knowledge and skills required to provide patients with optimal care. The program's aim is to promote professional development, lifelong learning and quality assurance for the public and medical community. However, physicians are not happy with the current structure of the program, claiming it to be time-consuming, expensive and ineffective for their practice. The lack of concrete evidence confirming the efficacy of MOC in improving knowledge and clinical outcomes causes many to question how this system can be improved to better serve practitioners and the public. In this commentary, we provide an overview of the current MOC situation for U.S. specialists and highlight the importance of increasing research to inform evidence-based changes that can be applied to clinical situations.
Strategic Inter-agency Capacity Building for Primary Prevention of Harmful Behaviors in the Military: Current and Future Directions
Gallagher S, Maxwell S, Jones K, Kelley LM and Fortson BL
The Department of Defense (DoD) remains committed to mitigating harmful behaviors that harm personnel and hinder military readiness. DoD's Sexual Assault Prevention and Response Office (SAPRO) and the Division of Violence Prevention (DVP) within the Centers for Disease Control and Prevention (CDC) established a partnership to build capacity for primary prevention though a wide-ranging training and technical assistance (TTA) system, The Integrated Prevention Technical Assistance Center (IPTAC). The system serves as a support system within the Interactive Systems Framework (ISF). The goal for IPTAC's TTA support is to build capacity for integrated primary prevention and build sustainability for prevention in complex military environments. To assess the effectiveness of IPTAC, the system is evaluated on what TTA is delivered, the skills and knowledge increase in TTA participants, participant satisfaction with TTA received, and participant application or intent for application of skills. Early results are positive; however, these results could be improved partly through ensuring a larger focus on tailoring to military contexts within all TTA activities. This article describes the creation of IPTAC, the role of the ISF in the implementation of TTA, and the evaluation of IPTAC. Implications for TTA delivery in the military and civilian sectors are discussed.
Improving School Mental Health via National Learning Collaboratives With State and Local Teams: Components, Feasibility, and Initial Impacts
Bohnenkamp J, Robinson P, Connors E, Carter T, Orenstein S, Reaves S, Hoover S and Lever N
School systems need practical and effective quality improvement strategies to advance school mental health promotion, prevention, and treatment services. Collectively, these efforts can be used to promote child and adolescent mental health, well-being, and academic success. The current study reports on the feasibility, initial impacts of, and recommendations from a national, multi-level learning collaborative conducted by the National Center for School Mental Health, University of Maryland School of Medicine and administered throughout the United States. The mixed-methods evaluation results support the feasibility of a learning collaborative and reinforce its positive initial impact on comprehensive school mental health system change. Participants indicated comprehensive school mental health quality improvements such as collaboration across diverse partners and spread of evidence-informed best practices that support high-quality services for students. The multi-level learning collaborative model is promising for future efforts to advance the dissemination of comprehensive school mental health systems and other state and local system change efforts. School mental health learning collaboratives may help address the ongoing youth mental health crisis by promoting high-quality mental health supports and services for youth.
The Technical Assistance (TA) Effectiveness Logic Model: A Tool for Systematically Planning, Delivering, and Evaluating TA
Scott VC, Chagnon E and Wandersman A
Technical assistance (TA) is a tailored approach to capacity building that has grown in use across diverse settings over the past two decades, particularly in the domains of health improvement, child welfare, youth development, and education. In practice, TA services often include a combination of activities (e.g., coaching, professional development, site visits, and resource sharing) and vary in dosage, modality, and numerous other dimensions. While tailoring to recipient needs holds significant value, the individualized nature of TA creates challenges for assessing the effectiveness of TA. The difficulty of determining what contributes to TA outcomes is amplified when TA delivery is largely reactive (rather than proactive) and unaccompanied by a systematic approach to planning, delivery, and evaluation. Logic models are a well-established tool and a straightforward way to make TA more systematic. In this article, we introduce the TA Effectiveness Logic Model as a skeletal framework to guide systematic TA planning, delivery, and evaluation. The TA Effectiveness Logic Model graphically presents the rationale and expectations for how TA works in a setting. We describe two types of TA effectiveness logic models: basic and contextual. In addition, we offer a case example from work based on a national training and TA center to illustrate both types of logic models. Lastly, we discuss practical implications of TA effectiveness logic models for TA collaborators (funders, training and TA center administrators, TA providers, TA recipients, and researchers). Routinizing the use of TA effectiveness logic models has benefits for both the science and practice of TA.
Commentary: The Need for Theories of Change in Training and Technical Assistance: Where the Rubber Meets the Road
Scheier LM
In this commentary, I revisit some of the core issues raised in both the first and second special issues on "Strengthening the Science and Practice of Implementation Support: Evaluating the Effectiveness of Training and Technical Assistance Centers." I first outline the concerns that I think are of paramount importance and then very briefly dissect each one from the perspective of a prevention scientist. I add commentary where I think the field can benefit and strengthen to advance the "science" of implementation support. At the same time, I also raise several points that I think will contribute to a better understanding of "how" TTA works, for "whom" and under what conditions. This portion of the commentary attends to the different training and learning modalities used for TTA, the argument that capacity building should be the objective, decluttering the constructs of motivation and readiness, and whether we can ever validly assess a public health impact from TTA. I offer suggestions to address each concern and hope that the field can benefit from this discussion as we usher in a new era.
Reducing Behavioral Problems and Treatment Duration of Adolescents in Secure Residential Care: A Multiple Single-Case Experimental Design Study
Gutterswijk RV, Kuiper CHZ, Harder AT, van der Horst FCP, Bocanegra BR and Prinzie P
Secure residential care (SRC) is criticized for several reasons. Therefore, in many countries, the general policy is to limit the length of stay of adolescents in SRC. However, research on length of stay and treatment effects of SRC on adolescents' behavioral problems is sparse. Using single case experimental designs with time-series, forty adolescents referred to SRC completed a questionnaire on behavioral and attention problems every two weeks during a baseline (A) and treatment period (B). Two-level regression analyses were used to investigate the effects of SRC on behavioral and attention problems. In addition, we tested whether length of stay moderated effectiveness. On the individual level, the treatment showed a positive statistically significant effect on the behavioral problems of 0%-8% of the adolescents and a statistically significant negative effect on behavioral problems was found in 3%-10% of the adolescents. On the group level, adolescents showed no significant decrease in problem behavior or attention problems from baseline to discharge. Length of stay did not moderate the results. Based on the results we conclude that most adolescents fail to improve. In addition, length of stay was not associated with effectiveness, nor could it be explained by adolescents' characteristics.
Improving Teacher-Child Relationships Using Relationship-Focused Reflection: A Case Study
Bosman RJ, de Jong PF and Koomen HMY
This study evaluated LLInC (Leerkracht-Leerling Interactie Coaching in Dutch, or Teacher Student Interaction Coaching), an intervention targeted at teachers' mental representations to improve dyadic teacher-child relationship quality. Four teachers and eight children from Dutch elementary schools participated in this single case study. Teachers themselves selected two children with whom they experienced a difficult relationship. The results indicated that teachers' global judgments of relationship quality improved from pretest to posttest for almost all teacher-child dyads. Day-to-day perceptions of conflict, closeness, and self-efficacy improved for a few teacher-child dyads, and especially for teacher-child dyads of the second targeted child. This implies that LLInC is especially helpful when carried out for at least two teacher-child dyads. The results of this study suggest that LLInC is promising, especially with regard to teachers' global relationship perceptions. However, LLInC should be further evaluated using a larger, representative sample, especially with regard to day-to-day perceptions of relationship quality.
Validity and Reliability of the Turkish Version of the Low Back Activity Confidence Scale (LoBACS)
Solum S and Salbaş E
The Low Back Activity Confidence Scale (LoBACS) is a 15-item scale designed to assess low back pain (LBP) through self-efficacy, a key predictor of functional recovery. This study aimed to culturally adapt and evaluate the validity and reliability of the Turkish version of LoBACS in patients with LBP. The translation and adaptation followed Beaton et al.'s protocol. Content and face validity were assessed with a pre-patient group. Both exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) were performed to evaluate construct validity. Internal consistency, as well as test-retest reliability, were evaluated in a sample of 150 patients aged 18-70 years. Concurrent validity was measured alongside the Oswestry Back Pain Disability Questionnaire (ODQ) and Quebec Back Pain Disability Scale (QBPDS). Two factors emerged from factor analysis, with item loadings for Functional Self-efficacy (FnSE) ranging from 0.745 to 0.896 and for Self-Regulatory and Exercise Self-efficacy (Self-Reg&ExSE) from 0.817 to 0.940. Cronbach's alpha was high for FnSE, Self-Reg&ExSE, and the total scale (α = 0.941). Total correlation for each item ranged between 0.770 and 0.925. Test-retest reliability was also high (r = 0.941, < .01). LoBACS showed moderate agreement with ODQ and QBPDS, demonstrating concurrent validity. In conclusion, the Turkish version of LoBACS is a valid and reliable tool for measuring LBP-related self-efficacy.
Using Generalized Linear Mixed Models in the Analysis of Count and Rate Data in Single-case Eperimental Designs: A Step-by-step Tutorial
Li H, Baek E, Luo W, Du W and Lam KH
Generalized linear mixed models (GLMMs) have great potential to deal with count and rate data in single-case experimental designs (SCEDs). However, applied researchers face challenges to apply such an advanced approach in their own studies. Hence, our study aimed to provide a tutorial and demonstrate a step-by-step procedure of using GLMMs to handle SCED count and rate outcomes. We utilized an empirical examplewith a purpose to examine the effect of prelinguistic milieu teaching (PMT) on prelinguistic intentional communication for six school-age children with autism. The outcomes were sustained intentional communication (frequency count) and initiated intentional communication (rate). A step-by-step analytical approach with GLMMs was illustrated and associated R and SAS code was provided. The results overall supported the original conclusions of the effectiveness of PMT, whereas additional evidence regarding the precise estimate of the individual treatment effect and between-case variation of the treatment effect were also interpreted. The implications of the similarities and differences between the findings based on GLMMs and from the original study were discussed.
Analyzing the Effects of a Repeated Reading Intervention on Reading Fluency With Generalized Linear Mixed Models
Li H, Avendaño SM and Bak MYS
In the United States, only approximately one-third of students read at or above proficiency level. Moreover, the difference in reading proficiency of students is severely disproportionate for students with disabilities compared to students without disabilities. Reading fluency is a precursor for academic success and one of the six aspects of reading that contributes to effective reading skills. Many studies have examined the effectiveness of repeated reading to improve reading fluency. However, existing literature has mixed evaluations of whether repeated reading can be considered evidence-based reading intervention practice for students with disabilities. The current study examined the effects of a repeated reading intervention on reading fluency for three middle school students with learning disabilities. To address limitations of traditional single-case experimental design analytical methods such as visual analysis and nonoverlap indices, our study provided empirical researchers with a step-by-step procedure of using an advanced statistical method for single-case experimental designs, namely, generalized linear mixed models (GLMM) to analyze data. The results presented by GLMMs showed that repeated reading intervention can significantly improve reading fluency for some students with learning disabilities. Implications, limitations, and future directions from both empirical and methodological perspectives were also discussed.
Single-Case Study of the Feasibility of Parent Training and Change in Parenting in Comparison to Baseline, in Adolescents With a Major Depressive Disorder
van den Brink C, Maric M, Niels H and Stikkelbroek Y
Existing research has shown that parental behavior can influence the onset and persistence of adolescent depression; however, the initial treatment guidelines do not include parental involvement, and there is no established protocol for engaging parents. For this study, the Doepressie parent training protocol was designed to teach parents ways to help their child cope with depression, and this study sought to evaluate the feasibility and changes in parenting of combining individual cognitive behavioral therapy (CBT) for adolescents with parent training. Because of the heterogeneity observed in adolescents with depression, a single-case design study with daily diaries for parents was conducted. Adolescents ( = 9; mean age = 15.9, SD = 1.05) with major depressive disorder and their parents participated in this study. Parents reported that the parent training was feasible. After treatment, two-thirds of the adolescents no longer met the criteria for major depressive disorder. Most of the parents reported positive effects on their child's mood and activity level, problem-solving skills with their child, and parental responsiveness and competence. Four parents demonstrated medium positive change. Involving parents in the treatment of adolescent depression has significant clinical benefits. Because of the heterogeneity of adolescent depression, the impact of parental involvement varies.
Evaluation of a Parenting Program for Mothers With a Borderline Personality Disorder: A Multiple Baseline Single-Case Experimental Design Study
Vigeveno DE, Maric M, Onghena P and Hupkes M
Parents with borderline personality disorder (BPD) experience deficiencies in parenting skills leading to increased family burden, stress, mental health problems in children and even family violence. The present study evaluated a Dutch version of the parenting training based on Dialectical Behavior Therapy (DBT) for mothers with BPD. A multiple baseline single-case experimental design study was conducted with standardized and idiosyncratic assessments of parenting behavior and parental stress before, biweekly during, and after training. Participants ( = 10) were mothers with a BPD diagnosis with a child under the age of 6. Four participants discontinued the training. Among six training completers, clinically reliable improvements in parenting skills were most pronounced for inconsistent discipline, involvement, positive parenting and corporal punishment. Frequent, idiosyncratic assessments showed that for six mothers training had a positive effect on parenting skills, while for five mothers this effect was large. Overall, less improvement was found for parenting stress. DBT parenting training seems to have clinical value for mothers with BPD struggling with raising their children. Most prominent improvement was found in relation to mothers disciplining their child in a more consistent manner. The complexity and heterogeneity of mothers with BPD requires a more idiosyncratic, patient-centered approach. This study was registered (retrospectively) in ISRCTN (ID ISRCTN74447767). https://www.isrctn.com/ISRCTN74447767, March 2022.
Embracing Complexity: Developing a Framework for Evaluating a Multi-Faceted Training and Technical Assistance System
Stanley AR, Jamison C, Chen A, Barranco L, Welsh D and Jones K
The benefits of training and technical assistance (TTA) have been well documented. There is limited literature that explores how complex systems of TTA are implemented and evaluated particularly in the violence prevention field. The Violence Prevention Practice and Translation Branch (VPPTB) within the Centers for Disease Control and Prevention's (CDC) Division of Violence Prevention funds multiple technical assistance providers who are tasked with building the capacity of program recipients to implement comprehensive approaches to prevent multiple forms of violence. VPPTB designed the Violence Prevention Technical Assistance Center (VPTAC) with the goal of implementing and evaluating comprehensive TTA efforts that integrates the work of multiple TTA providers to build the capacity of recipients to plan, implement, and evaluate violence prevention efforts. The VPTAC evaluation incorporates data from program recipients, TTA providers, and TTA modalities enabling the VPPTB staff to show improvement in technical knowledge, gather examples of enhanced implementation, and facilitate proactive TTA planning. An important step in the process of evaluating VPTAC from a system-level perspective required an expansion beyond evaluating a single TTA event, provider, or engagement. This is essential to understand how a diverse set of TTA activities and partners work together in their efforts to build capacity.
Evidence-Based Implementation Support: Considering Motivation and Capacity Within the Ecosystem of Training and Technical Assistance
Bumbarger BK, Moore JE and Crane ME
This invited commentary reflects on Wandersman and Scheier's (2024) call for a more evidence-based model of training and technical assistance (i.e. TTA or implementation support). Their clarion call prompts us to consider what steps need to be taken to refine and scale a solution that genuinely enhances the effectiveness of TTA through a re-imagined model of implementation support. We highlight eight priorities to re-imagine a more effective and efficient model of TTA that reflects best practice and simultaneously contributes to continuous, collective evidence-building. The eight priorities include: (1) an ecosystem of TTA connecting TTA research and practice; (2) TTA capacity building; (3) health equity, and equitable partnerships; (4) trust and relationships; (5) TTA evaluation; (6) continuous quality improvement; (7) implementation support mechanisms; and (8) cost-effective solutions. We advocate for an international, cross-disciplinary, applied agenda aimed at establishing a robust empirical foundation for TTA to foster a culture of continuous quality improvement and knowledge generation across government agencies and philanthropies that fund TTA Centers. We describe a potential scenario for how funders can initiate and support evidence-based TTA.
Advancing the Science and Practice of Training and Technical Assistance to Improve the Equitable Implementation of Evidence-Based Practices
Acosta J, Shearer A and Chinman M
Health inequities in the US are greater than those in other industrialized countries and have shown little improvement over the past 20 years. Training and technical assistance centers (TTACs) could be a potential mechanism to address inequities, but to date, have lacked an explicit equity-focus. In this paper we describe how to apply equitable implementation strategies when using an evidence-based training and technical assistance process (Getting To Outcomes) and offer the Health Equity Interactive Systems Framework to support the dissemination and implementation of readily applicable equitable implementation strategies. Proposed improvements to implementation strategies' equity focus could provide a scalable way for TTACs to promote implementation strategies that are equity-focused. Findings could also inform continuous quality improvement frameworks used by TTACs to close the research to practice gap and make progress towards reducing health inequities.
Commentary: Strengthening System Readiness for Health Interventions: Lessons for Implementing Interventions and Implementation Support in Low-And Middle-Income Countries
Chen H, Chuengsatiansup K, Wong DR, Sihapark S, Krisanaprakornkit T, Wisetpholchai B, Tongsiri S, Hinton L, Gallagher-Thompson D, Wandersman A, Marques AH, Lamont AE and Levkoff SE
In low- and middle-income countries (LMICs), barriers such as low system readiness, contextual mismatches, and resource limitations impede effective implementation of evidence-based interventions. This commentary offers insights into overcoming these challenges with a case study of the PRISM project, designed to reduce behavioral and psychological symptoms of dementia in older adults living in Thailand. The case highlights how combining two evidence-based models - the clinical intervention and the implementation science process enhances program success. Using interviews with stakeholders across various health system levels, we identify factors critical to successful program implementation: (1) integrating interventions into policy frameworks, (2) empowering local implementers, (3) fostering collaborative learning, and (4) adapting interventions to local contexts. The case demonstrates that building system readiness through local engagement and ownership is central to scaling up health programs in LMICs. This commentary's contribution lies in its emphasis on the role of implementation science as a vehicle for translating research into practice. It presents a practical, adaptive model for embedding interventions into routine health systems, thereby offering a pathway for successfully scaling up evidence-based programs in LMICs. Such findings provide lessons for overcoming barriers to implementation in resource-limited environments.
Commentary: Bridging and Reducing the Gaps Between Research and Practice: Pathways to Outcomes and the Interactive Systems Framework for Dissemination and Implementation 2.0
Wandersman A, Cook BS, Clark K, Flaspohler P, Watson A and Lamont AE
There are many ways proposed to achieve better societal outcomes (e.g., in health, education, and well-being) including: (1) bridging research and practice, (2) building the motivation and capacity of service delivery organizations (e.g., schools, hospitals, clinics, and community-based organizations) to innovate, and (c) providing service delivery systems with high-quality support via training and technical assistance. The Interactive Systems Framework for Dissemination and Implementation (ISF) was developed to describe how relevant systems, organizations, and processes can interact and work toward these goals. Stimulated by the 13 articles contained in the two special issues of , we describe several enhancements to the ISF including: how service delivery systems can operate better, how motivation and capacity can be built, and how training and technical assistance centers can provide more evidence-informed technical assistance and other promising innovations. ISF 2.0 incorporates these and other enhancements with the goal of achieving better outcomes. We conclude that the actions and accountability of funders and of organizations and systems to funders would accelerate progress in the systems to achieve outcomes-and result in improving the science and practice of implementation support.
Mindful With Your Baby/Toddler: A Single Case Design (SCD) Study
Schaeffer MA and Potharst ES
Transitioning to motherhood comes with new and intensive tasks that may cause parental stress, low parental self-efficacy, and internalizing problems. This can in turn negatively affect the mother-child relationship. Mindful with your Baby/Toddler (MwyB/T) is a mindfulness-based intervention for parents of young children experiencing parental stress and internalizing problems. Previous evaluative studies showed promising results, but methodology of these studies was limited. The current study used a single case design, including a baseline, intervention, posttest, and follow-up phase, to evaluate the effectiveness of MwyB/T. Ten participants were included and completed daily administered personalized items and validated questionnaires measuring mindfulness, mindful parenting, parental self-efficacy, internalizing problems, and parental stress, for 10 participants. Personalized items were first coded into themes and then assessed using visual analysis and descriptive effect size measures. Reliable change indices were computed for the questionnaires. All mothers improved on personalized items, with most improving on most (or all) of their items. On the questionnaires the majority of mothers improved. Results indicate that MwyB/T could benefit mothers with various intervention goals. More research is needed on the role of personalized items, both as a research measure and an as a possible additional element of interventions.
Behavioral Addiction Treatment Centers in the Hospitals of Türkiye: A Web-Based Research
Doğan Keskin A, Öztürk N, Düştü F and Yilmaz B
This study investigates the current landscape of behavioral addiction treatment in Türkiye hospitals, considering both inpatient and outpatient approaches. The analysis involved examining the websites of 1393 hospitals across Türkiye based on various criteria. The review of the websites was conducted between June and September 2023. The findings reveal that out of these hospitals, comprising 822 public and 571 private institutions, only 51 provide treatment for behavioral addictions. Behavioral addiction treatments are available in 23 of the 81 provinces in Türkiye, and 24 out of the 51 hospitals offering treatment for behavioral addictions are located in İstanbul (47.1%), while three (5.9%) are located in Ankara. Among these 51 hospitals, 22 are public, and 29 are private. The primary focus of treatment revolves around internet and gambling addiction. Upon analyzing the patient groups served, it was observed that 49% ( = 25) of the hospitals specialize in treating adult patients, while 29.4% ( = 15) cater to pediatric patients. While the websites of 11 hospitals contain information about the behavioral addiction treatments offered, they lack any information on the patient groups to which they cater. The predominant treatment modalities include psychotherapy (25.49%), followed by psychopharmacotherapy (19.61%) and cognitive-behavioral therapy (17.65%). In conclusion, the treatment of behavioral addictions, such as those related to the internet, gaming, and shopping, are offered in hospitals across various regions and age groups. Considering that only 3.7% of hospitals in Türkiye treat behavioral addictions, this type of treatment is not widespread.
Estimating Mediation Effects in ABAB Reversal Designs
Valente MJ, Pang J, Rijnhart JJM, Ferron J and Miočević M
Single-Case Experimental Designs (SCEDs), or N-of-1 trials, are commonly used to estimate intervention effects in many disciplines including in the treatment of youth mental health problems. SCEDs consist of repeated measurements of an outcome over time for a single case (e.g., student or patient) throughout one or more baseline phases and throughout one or more intervention phases. The manipulation of the baseline and intervention phase make the SCED a type of interrupted time series design, which is considered one of the most effective experimental designs for causal inference. An important step towards understanding why interventions are effective at producing a change in the outcome is through the investigation of mediating mechanisms. Hypotheses of mediating mechanisms involve an intervention variable which is hypothesized to affect an outcome through its effect on a mediating variable. Little work has attempted to combine mediation analysis and ABAB reversal designs. Therefore, the goals of this paper are to define, estimate, and interpret mediation effects for ABAB reversal designs. An empirical example is used to demonstrate how to estimate and interpret the mediation effects. R code is provided for researchers interested in estimating mediation effects in single-case reversal designs.