Interventions to improve team effectiveness within health care: a systematic review of the past decade

Background A high variety of team interventions aims to improve team performance outcomes. In 2008, we conducted a systematic review to provide an overview of the scientific studies focused on these interventions. However, over the past decade, the literature on team interventions has rapidly evolved. An updated overview is therefore required, and it will focus on all possible team interventions without restrictions to a type of intervention, setting, or research design. Objectives To review the literature from the past decade on interventions with the goal of improving team effectiveness within healthcare organizations and identify the “evidence base” levels of the research. Methods Seven major databases were systematically searched for relevant articles published between 2008 and July 2018. Of the original search yield of 6025 studies, 297 studies met the inclusion criteria according to three independent authors and were subsequently included for analysis. The Grading of Recommendations, Assessment, Development, and Evaluation Scale was used to assess the level of empirical evidence. Results Three types of interventions were distinguished: (1) Training, which is sub-divided into training that is based on predefined principles (i.e. CRM: crew resource management and TeamSTEPPS: Team Strategies and Tools to Enhance Performance and Patient Safety), on a specific method (i.e. simulation), or on general team training. (2) Tools covers tools that structure (i.e. SBAR: Situation, Background, Assessment, and Recommendation, (de)briefing checklists, and rounds), facilitate (through communication technology), or trigger (through monitoring and feedback) teamwork. (3) Organizational (re)design is about (re)designing structures to stimulate team processes and team functioning. (4) A programme is a combination of the previous types. The majority of studies evaluated a training focused on the (acute) hospital care setting. Most of the evaluated interventions focused on improving non-technical skills and provided evidence of improvements. Conclusion Over the last decade, the number of studies on team interventions has increased exponentially. At the same time, research tends to focus on certain interventions, settings, and/or outcomes. Principle-based training (i.e. CRM and TeamSTEPPS) and simulation-based training seem to provide the greatest opportunities for reaching the improvement goals in team functioning.


Introduction
Teamwork is essential for providing care and is therefore prominent in healthcare organizations. A lack of teamwork is often identified as a primary point of vulnerability for quality and safety of care [1,2]. Improving teamwork has therefore received top priority. There is a strong belief that effectiveness of healthcare teams can be improved by team interventions, as a wide range of studies have shown a positive effect of team interventions on performance outcomes (e.g. effectiveness, patient safety, efficiency) within diverse healthcare setting (e.g. operating theatre, intensive care unit, or nursing homes) [3][4][5][6][7].
In light of the promising effects of team interventions on team performance and care delivery, many scholars and practitioners evaluated numerous interventions. A decade ago (2008), we conducted a systematic review with the aim of providing an overview of interventions to improve team effectiveness [8]. This review showed a high variety of team interventions in terms of type of intervention (i.e. simulation training, crew resource management (CRM) training, interprofessional training, general team training, practical tools, and organizational interventions), type of teams (e.g. multi-, mono-, and interdisciplinary), type of healthcare setting (e.g. hospital, elderly care, mental health, and primary care), and quality of evidence [8]. From 2008 onward, the literature on team interventions rapidly evolved, which is evident from the number of literature reviews focusing on specific types of interventions. For example, in 2016, Hughes et al. [3] published a meta-analysis demonstrating that team training is associated with teamwork and organizational performance and has a strong potential for improving patient outcomes and patient health. In 2016, Murphy et al. [4] published a systematic review, which showed that simulation-based team training is an effective method to train a specific type of team (i.e. resuscitation teams) in the management of crisis scenarios and has the potential to improve team performance. In 2014, O'Dea et al. [9] showed with their meta-analysis that CRM training (a type of team intervention) has a strong effect on knowledge and behaviour in acute care settings (as a specific healthcare setting). In addition to the aforementioned reviews, a dozen additional literature reviews that focus on the relationship between (a specific type of) team interventions and team performance could be mentioned [7,[10][11][12][13][14][15][16][17][18][19]. In sum, the extensive empirical evidence shows that team performance can be improved through diverse team interventions.
However, each of the previously mentioned literature reviews had a narrow scope, only partly answering the much broader question of how to improve team effectiveness within healthcare organizations. Some of these reviews focus on a specific team intervention, while others on a specific area of health care. For example, Tan et al. [7] presented an overview on team simulation in the operating theatre and O'Dea et al. [9] focused on CRM intervention in acute care. Other reviews only include studies with a certain design. For instance, Fung et al. [13] included only randomized controlled trials, quasi-randomized controlled trials, controlled before-after studies, or interrupted time series. Since the publication of our systematic review in 2010 [8], there has been no updated overview of the wide range of team interventions without restrictions regarding the type of team intervention, healthcare setting, type of team, or research design. Based on the number and variety of literature reviews conducted in recent years, we can state that knowledge on how to improve team effectiveness (and related outcomes) has progressed quickly, but at the same time is quite scattered. An updated systematic review covering the past decade is therefore relevant.
The purpose of this study is to answer two research questions: (1) What types of interventions to improve team effectiveness (or related outcomes) in health care have been researched empirically, for which setting, and for which outcomes (in the last decade)? (2) To what extent are these findings evidence based?

Inclusion and exclusion criteria
This systematic review aims to capture the full spectrum of studies that empirically demonstrate how healthcare organizations could improve team effectiveness. Therefore, the following studies were excluded: 1. Studies outside the healthcare setting were excluded. Dental care was excluded. We did not restrict the review to any other healthcare setting. 2. Studies without (unique) empirical data were excluded, such as literature reviews and editorial letters. Studies were included regardless of their study design as long as empirical data was presented. Book chapters were excluded, as they are not published in peer-reviewed journals. 3. Studies were excluded that present empirical data but without an outcome measure related to team functioning and team effectiveness. For example, a study that evaluates a team training without showing its effect on team functioning (or care provision) was excluded because it does not provide evidence on how this team training affects team functioning. 4. Studies were excluded that did not include a team intervention or that included an intervention that did not primarily focus on improving team processes, which is likely to enhance team effectiveness (or other related outcomes). An example of an excluded study is a training that aims to improve technical skills such as reanimation skills within a team and sequentially improves communication (without aiming to improve communication). It is not realistic that healthcare organizations will implement this training in order to improve team communication. Interventions in order to improve collaboration between teams from different organizations were also eliminated. 5. Studies with students as the main target group. An example of an excluded study is a curriculum on teamwork for medical students as a part of the medical training, which has an effect on collaboration. This is outside the scope of our review, which focuses on how healthcare organizations are able to improve team effectiveness.
In addition, how teams were defined was not a selection criterion. Given the variety of teams in the healthcare field, we found it acceptable if studies claim that the setting consists of healthcare teams. Figure 1 summarizes the search and screening process according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) format. A four-stage process was followed to select potential articles. We started with 6025 articles. First, each title and abstract was subjected to elimination based on the aforementioned inclusion and exclusion criteria. Two reviewers reviewed the title/abstracts independently. Disagreement between the reviewers was settled by a third reviewer. In case of doubt, it was referred to the next stage. The first stage reduced the number of hits to 639. Second, the full text articles were assessed for eligibility according to the same set of elimination criteria. After the full texts were read by two reviewers, 343 articles were excluded. In total, 297 articles were included in this review. Fourth, the included articles are  Table 1. Each article is described using the following structure:

Selection process
-Type of intervention -Setting: the setting where the intervention is introduced is described in accordance with the article, without further categorization -Outcomes: the effect of the intervention -Quality of evidence: the level of empirical evidence is based in the Grading of Recommendations Assessment Development, and Evaluation (GRADE) scale. GRADE distinguishes four levels of quality of evidence A. High: future research is highly unlikely to change the confidence in the estimated effect of the intervention. B. Moderate: future research is likely to have an important impact on the confidence in the estimated effect of the intervention and may change it. C. Low: future research is very likely to have an important impact on the confidence in the estimated effect of the intervention and is likely to change it. D. Very low: any estimated effect of the intervention is very uncertain.
Studies can also be upgraded or downgraded based on additional criteria. For example, a study is downgraded by one category in the event there are important inconsistencies. Detailed information is provided as additional material (see Additional file 2).

Organization of results
The categorization of our final set of 297 articles is the result of three iterations. First, 50 summarized articles were categorized using the initial categorization: team training (subcategories: CRM-based training, simulation training, interprofessional training, and team training), tools, and organizational intervention [8]. Based on this first iteration, the main three categories (i.e. training, tools, and organizational interventions) remained unchanged but the subcategorization was further developed. Training, related to the subcategory "CRM-based training", "TeamSTEPPS" was added as a subcategory. The other subcategories (i.e. simulation training, interprofessional training, and team training) remained the same. Tools, the first draft of subcategories, entailed Situation, Background, Assessment, and Recommendation (SBAR), checklists, (de)briefing, and task tools. Two subcategories of organizational intervention (i.e. programme and (re)design) were created, which was also in line with the content of this category in the original literature review. Second, 50 additional articles were categorized to test and refine the subcategories. Based on this second iteration, the subcategories were clustered, restructured and renamed, but the initial three main categorizations remained unaffected. The five subcategories of training were clustered into principle-based training, method-based training, and general team training. The tools subcategories were clustered into structuring, facilitating, and triggering tools, which also required two new subcategories: rounds and technology. Third, the remaining 197 articles were categorized to test the refined categorization. In addition, the latter categorization was peer reviewed. The third iteration resulted in three alterations. First, we created two main categories based on the two subcategories "organizational (re)design" and "programme" (of the third main categorization). Consequently, we rephrased "programme-based training" into "principle-based training". Second, the subcategories "educational intervention" and "general team training" were merged into "general team training". Consequently, we rephrased "simulation training" into "simulation-based training". Third, we repositioned the subcategories "(de)briefing" and "rounds" as structuring tools instead of facilitating tools. Consequently, we merged the subcategories "(de)briefing" and "checklists" into "(de)briefing checklists". Thereby, the subcategory "technology" became redundant.

Results
Four main categories are distinguished: training, tools, organizational (re)design, and programme. The first category, training, is divided in training that is based on specific principles and a combination of methods (i.e. CRM and Team Strategies and Tools to Enhance Performance and Patient Safety (TeamSTEPPS)), a specific training method (i.e. training with simulation as a core element), or general team training, which refers to broad team training in which a clear underlying principle or specific method is not specified. The second category, tools, are instruments that are introduced to improve teamwork by structuring (i.e. SBAR (Situation, Background, Assessment, and Recommendation), (de)briefing checklists, and rounds), facilitating (through communication technology), or triggering (through monitoring and feedback) team interaction. Structuring tools partly standardize the process of team interaction. Facilitating tools provide better opportunities for team interaction. Triggering tools provide information to incentivize team interaction. The third category, organizational (re)design, refers to (re)designing structures (through implementing pathways, redesigning schedules, introducing or redesigning roles and responsibilities) that will lead to improved team processes and functioning. The fourth category, a programme, refers to a combination of the                     [292] Innovative compensation model: replaced fee-for-service payment with a largely team based, qualityfocused payment, 40% of compensation was based upon the clinic-

Primary care
Mixed results: quality improvement for the team and less patient "dumping," or shifting patients with poor outcomes to other clinicians, but also lack of control and C  previous types of interventions (i.e. training, tools, and/ or redesign). Table 2 presents the (sub)categorization, number of studies, and a short description of each (sub)category.

Overall findings Type of intervention
The majority of studies evaluated a training. Simulationbased training is the most frequently researched type of team training.

Setting
Most of the articles researched an acute hospital setting. Examples of acute hospital settings are the emergency department, operating theatre, intensive care, acute elderly care, and surgical unit. Less attention was paid to primary care settings, nursing homes, elderly care, or long-term care in general.

Outcome
Interventions focused especially on improving nontechnical skills, which refer to cognitive and social skills such as team working, communication, situational awareness, leadership, decision making, and task management [21]. Most studies relied on subjective measures to indicate an improvement in team functioning, with only a few studies (also) using objective measures. The Safety Attitude Questionnaire (SAQ) and the Non-Technical Skills (NOTECHS) tool are frequently used instruments to measure perceived team functioning.

Quality of evidence
A bulk of the studies had a low level of evidence. A preand post-study is a frequently used design. In recent years, an increasing number of studies have used an action research approach, which often creates more insight into the processes of implementing and tailoring an intervention than the more frequently used designs (e.g. Random Control Trial and pre-post surveys). However, these valuable insights are not fully appreciated within the GRADE scale. The findings per category will be discussed in greater detail in the following paragraphs. Training CRM and TeamSTEPPS are well-known principle-based trainings that aim to improve teamwork and patient safety in a hospital setting. Both types of training are based on similar principles. CRM is often referred to as a training intervention that mainly covers non-technical skills such as situational awareness, decision making, teamwork, leadership, coping with stress, and managing fatigue. A typical CRM training consists of a combination of information-based methods (e.g. lectures), demonstration-based methods (e.g. videos), and practice-based methods (e.g. simulation, role playing) [9]. However, CRM has a management concept at its core that aims to maximize the use of all available resources (i.e. equipment, time, procedures, and people) [324]. CRM aims to prevent and manage errors through avoiding errors, trapping errors before they are committed, and mitigating the consequences of errors that are not trapped [325]. Approximately a third of CRM-based trainings include the development, redesign or implementation of learned CRM techniques/tools (e.g. briefing, debriefing, checklists) and could therefore also be categorized in this review under programme [39,40,42,51,56,58,59,61,62]. The studies show a high variety in the content of CRM training and in the results measured. The majority of the studies claim an improvement in a number of non-technical skills that were measured, but some also show that not all non-technical skills measured were improved [43,47,66]. Moreover, the skills that did or did not improve differed between the studies. A few studies also looked at outcome measures (e.g. clinical outcomes, error rates) and showed mixed results [49,52,53]. Notable is the increasing attention toward nursing CRM, which is an adaptation of CRM to nursing units [66,67]. Most studies delivered a low to moderate quality level of evidence. Although most studies measured the effect of CRM over a longer period of time, most time periods were limited to one or two evaluations within a year. Savage et al. [58] and Ricci et al. [56] note the importance of using a longer time period.
As a result of experienced shortcomings of CRM, Team Strategies and Tools to Enhance Performance and Patient Safety (TeamSTEPPS) has evolved (since 2006). TeamSTEPPS is a systematic approach designed by the Agency for Healthcare Research and Quality (AHRQ) and the Department of Defense (DoD) to enhance teamwork skills that are essential to the delivery of quality and safe care. Some refer to TeamSTEPPS as "CRM and more". TeamSTEPPS provides an approach on preparing, implementing, and sustaining team training. It is provided as a flexible training kit and facilitates in developing a tailored plan. It promotes competencies, strategies, and the use of standardized tools on five domains of teamwork: team structure, leadership, communication, situational monitoring, and mutual support. In addition, TeamSTEPPS focuses on change management, coaching, measurement, and implementation. Notable is that even though the TeamSTEPSS training is most likely to differ across settings as it needs to be tailored to the situational context, articles provide limited information on the training content.
All studies report improvements in some nontechnical skills (e.g. teamwork, communication, safety culture). Combining non-technical skills with outcome measures (e.g. errors, throughput time) seemed more common in this category. Half of the studies delivered a moderate to high quality of evidence.
Simulation-based training uses a specific method as its core, namely, simulation, which refers to "a technique to replace or amplify real-patient experiences with guided experiences, artificially contrived, that evokes or replicates substantial aspects of the real world in a fully interactive manner" [326]. The simulated scenarios that are used can have different forms (e.g. in situ simulation, in centre simulation, human actors, mannequin patients) and are built around a clinical scenario (e.g. resuscitation, bypass, trauma patients) aiming to improve technical and/or nontechnical skills (e.g. interprofessional collaboration, communication). We only identified studies in a hospital setting, which were mostly focussed on an emergency setting. All studies reported improvements in some non-technical skills (e.g. teamwork behaviour, communication, shared mental model, clarity in roles and responsibilities). In addition, some studies report non-significant changes in non-technical skills [98,137,140,155]. Some studies also looked at technical skills (e.g. time spend) and presented mixed results [63,112,152,159]. Sixty-nine studies focused on simulation-based training, of which 16 studies delivered a moderate to high quality of evidence.
General team training does not focus on one specific training principle or method. It often contains multiple educational forms such as didactic lectures, interactive sessions, and online modules. General team training focuses on a broad target group and entails for example team building training, coaching training, and communication skills training. Due to the broad scope of this category, high variation in outcomes is noted, although many positive outcomes were found. Most studies have a low to very low level of evidence.

Tools
Tools are instruments that could be implemented relatively independently in order to structure, facilitate or trigger teamwork.

Structuring tools
Teamwork can be structured by using the structured communication technique SBAR (Situation, Background, Assessment, and Recommendation), (de)briefing checklists, and rounds.
SBAR is often studied in combination with strategies to facilitate implementation, such as didactic sessions, training, information material, and modifying SBAR material (e.g. cards) [202,204,[206][207][208]211]. In addition, this subcategory entails communication techniques similar or based on SBAR [203,205,209,210,212]. One study focused on nursing homes, while the remaining studies were performed in a hospital setting. Most studies found improvements in communication; however, a few found mixed results [208,209]. Only (very) low-level evidence studies were identified.
Briefings and debriefings create an opportunity for professionals to systematically communicate and discuss (potential) issues before or after delivering care to a patient, based on a structured format of elements/topics or a checklist with open and/or closed-end questions. Studies on (de)briefing checklists often evaluate the implementation of the World Health Organization surgical safety checklist (SSC), a modified SSC, SSC-based checklist, or a safety checklist in addition to the SSC. The SSC consists of a set of questions with structured answers that should be asked and answered before induction of anaesthesia, before skin incision, and before the patient leaves the operating theatre. In addition, several studies presented checklists aiming to better manage critical events [221,223,233]. Only one study on SSC was conducted outside the surgery department/operating theatre (i.e. cardiac catheterization laboratory [222]). However, similar tools can also be effective in settings outside the hospital, as shown by two studies that focused on the long-term care setting [249,260]. Overall, included studies show that (de)briefing checklists help improve a variety of non-technical skills (e.g. communication, teamwork, safety climate) and objective outcome measures (e.g. reduced complications, errors, unexpected delays, morbidity). At the same time, some studies show mixed results or are more critical of its (sustainable) effect [215,222,231,242]. Whyte et al. [262] pointed out the complexity of this intervention by presenting five paradoxical findings: team briefings could mask knowledge gaps, disrupt positive communication, reinforce professional divisions, create tension, and perpetuate a problematic culture. The quality of evidence varied from high to very low (e.g. Whyte et al. [262]), and approximately one third presented a high or moderate quality of evidence. Debriefings can also be used as part of a training, aiming to provide feedback on trained skills. Consequently, some articles focused on the most suitable type of debriefing in a training setting (e.g. video-based, selfled, instructor-led) [245,246,253,263] or debriefing as reflection method to enhance performance [258,261].
Rounds can be described as structured interdisciplinary meetings around a patient. Rounds were solely researched in hospital settings. Five studies found improvements in non-technical skills, one study in technical skills, and one study reported outcomes but found no improvement. Three studies presented a moderate level of evidence, and the others presented a (very) low level.

Facilitating tools
Teamwork can be facilitated through technology. Technology, such as telecommunication, facilitates teamwork as it creates the opportunity to involve and interact with professionals from a distance [271][272][273]. Technology also creates opportunities to exchange information through information platforms [276,277]. Most studies found positive results for teamwork. Studies were performed in a hospital setting and presented a level of evidence varying from moderate to very low.

Triggering tools
Teamwork could be triggered by tools that monitor and visualize information, such as (score) cards and dashboards [278,279,281,283,284]. The gathered information does not echo team performance but creates incentives for reflecting on and improving teamwork. Team processes (e.g. trust, reflection) are also triggered by sharing experiences, such as clinical cases and stories, thoughts of the day [280,282]. All seven studies showed improvements in non-technical skills and had a very low level of evidence.

Organizational (re)design
In contrast with the previous two categories, organizational (re)design is about changing organizational structures. Interventions can be focused on several elements within a healthcare organization, such as the payment system [292] and the physical environment [299], but are most frequently aimed at standardization of processes in pathways [286,288] and changing roles and responsibilities [287,289,298], sometimes by forming dedicated teams or localizing professionals to a certain unit or patient [290,291,295,300]. Most studies found some improvements of non-technical skills; however, a few found mixed results. Only four studies had a moderate level of evidence, and the others had a (very) low level.

Programme
A programme most frequently consists of a so-called Human Resource Management bundle that combines learning and educational sessions (e.g. simulation training, congress, colloquium), often multiple tools (e.g. rounds, SBAR), and/or structural intervention (e.g. meetings, standardization). Moreover, a programme frequently takes the organizational context into account: developing an improvement plan and making choices tailored to the local situation. A specific example is the "Comprehensive Unit-Based Safety Program" (CUSP) that combines training (i.e. science of safety training educational curriculum, identify safety hazards, learn from defects) with the implementation of tools (e.g. team-based goal sheet), and structural intervention (i.e. senior executive partnership, including nurses on rounds, forming an interdisciplinary team) [309,319,322]. Another example is the medical team training (MTT) programme that consists of three stages: (1) preparation and follow-up, (2) learning session, (3) implementation and follow-up. MTT combines training, implementation of tools (briefings, debriefing, and other projects), and follow-up coaching [5,304,305,316]. MMT programmes are typically based on CRM principles, but they distinguish themselves from the first category by extending their programme with other types of interventions. Most studies focus on the hospital setting, with the exception of the few studies performed in the primary care, mental health care, and healthcare system. Due to the wide range of programmes, the outcomes were diverse but mostly positive. The quality of evidence varied from high to very low.

Conclusion and discussion
This systematic literature review shows that studies on improving team functioning in health care focus on four types of interventions: training, tools, organizational (re)design, and programmes. Training is divided into principle-based training (subcategories: CRM-based training and Team-STEPPS), method-based training (simulation-based training), and general team training. Tools are instruments that could be implemented relatively independently in order to structure (subcategories: SBAR, (de)briefing checklists, and rounds), facilitate (through communication technology), or trigger teamwork (through information provision and monitoring). Organizational (re)design focuses on intervening in structures, which will consequently improve team functioning. Programmes refer to a combination of different types of interventions.
Training is the most frequently researched intervention and is most likely to be effective. The majority of the studies focused on the (acute) hospital care setting, looking at several interventions (e.g. CRM, Team-STEPPS, simulation, SBAR, (de)briefing checklist). Longterm care settings received less attention. Most of the evaluated interventions focused on improving nontechnical skills and provided evidence of improvements; objective outcome measures also received attention (e.g. errors, throughput time). Looking at the quantity and quality of evidence, principle-based training (i.e. CRM and TeamSTEPPS), simulation-based training, and (de)briefing checklist seem to provide the biggest chance of reaching the desired improvements in team functioning. In addition, programmes, in which different interventions are combined, show promising results for enhancing team functioning. The category programmes not only exemplify this trend, but are also seen in principle-based training.
Because this review is an update of our review conducted in 2008 (and published in 2010) [8], the question of how the literature evolved in the last decade arises. This current review shows that in the past 10 years significantly more research has focused on team interventions in comparison to the previous period. However, the main focus is on a few specific interventions (i.e. CRM, simulation, (de)briefing checklist). Nevertheless, an increasing number of studies are evaluating programmes in which several types of interventions are combined.
Training: There has been a sharp increase in research studying team training (from 32 to 173 studies). However, the majority of these studies still look at similar instruments, namely, CRM-based and simulation-based training. TeamSTEPPS is a standardized training that has received considerable attention in the past decade. There is now a relatively strong evidence for the effectiveness of these interventions, but mostly for the (acute) hospital setting. Tools: There is also a substantial increase (from 8 to 84 studies) in studies on tools. Again, many of these studies were in the same setting (acute hospital care) and focused on two specific tools, namely, the SBAR and (de)briefing checklist. Although the level of evidence for the whole category tools is ambiguous, there is relatively strong evidence for the effectiveness of the (de)briefing checklist. Studies on tools that facilitate teamwork ascended the past decade. There is limited evidence that suggests these may enhance teamwork. The dominant setting was again hospital care, though triggering tools were also studied in other settings such as acute elderly care and clinical primary care. Moreover, most studies had a (very) low quality of evidence, which is an improvement compared to the previous review that solely presented (very) low level of evidence. Organizational (re)design: More attention is paid to organizational (re)design (from 8 to 16 studies). Although the number of studies on this subject has increased, there still remains unclarity about its effects because of the variation in interventions and the mixed nature of the results. Programmes: There seems to be new focus on a programmatic approach in which training, tools, and/or organizational (re)design are combined, often focused around the topic patient safety. The previous review identified only one such study; this research found 24 studies, not including the CRM studies for which some also use a more programmatic approach. There seems to be stronger evidence that this approach of combining interventions may be effective in improving teamwork.

Limitations
The main limitation of this review is that we cannot claim that we have found every single study per subcategory. This would have required per subcategory an additional systematic review or an umbrella review, using additional keywords. As we identified a variety of literature reviews, future research should focus on umbrella reviews in addition to new systematic literature reviews. Note that we did find more studies per subcategory, but they did not meet our inclusion criteria. For example, we excluded multiple studies evaluating surgical checklists that did not measure its effect on team functioning but only on reported errors or morbidity. Although this review presents all relevant categories to improve team functioning in healthcare organizations, those categories are limited to team literature and are not based on related research fields such as integrated care and network medicine. Another limitation is that we excluded grey literature by only focusing on articles written in English that present empirical data and were published in peerreviewed journals. Consequently, we might have excluded studies that present negative or non-significant effects of team interventions, and such an exclusion is also known as publication bias. In addition, the combination of the publication bias and the exclusion of grey literature has probably resulted in a main focus on standardized interventions and a limited range of alternative approaches, which does not necessarily reflect practice.

Implication for future research
This review shows the major increase in the last decade in the number of studies on how to improve team functioning in healthcare organizations. At the same time, it shows that this research tends to focus around certain interventions, settings, and outcomes. This helped to provide more evidence but also left four major gaps in the current literature. First, less evidence is available about interventions to improve team functioning outside the hospital setting (e.g. primary care, youth care, mental health care, care for disabled people). With the worldwide trend to provide more care at home, this is an important gap. Thereby, team characteristics across healthcare settings vary significantly, which challenges the generalizability [327]. Second, little is known about the long-term effects of the implemented interventions. We call for more research that monitors the effects over a longer period of time and provides insights into factors that influence their sustainability. Third, studies often provide too little information about the context. To truly understand why a team intervention affects performance and to be able to replicate the effect (by researchers and practitioners), detailed information is required related to the implementation process of the intervention and the context. Fourth, the total picture of relevant outcomes is missing. We encourage research that includes less frequently used outcomes such as well-being of professionals and focuses on identifying possible deadly combinations between outcomes.