The studies concerning psychotherapy effectiveness have made much progress, mainly by proving—through rigorous investigations—that this care form can be effective for patients, and that different clinical-theoretical models show similar results [5] .

In literature, this research topic follows the distinction between studies on outcomes (which evaluate both the overall efficacy and the different forms of efficacy of specific clinical models) and the studies on the process (the mechanisms of change that operate within the therapeutic pathway).

As for the outcome analysis, the research has mainly been directed toward the effectiveness assessment of the specific clinical models. A large number of empirical and evidence-based researches concern the behavioral-cognitivist models. Tolin [6] proposed a quantitative review concerning the efficacy of Cognitive-Behavioral Therapy (CBT) in comparison with other forms of psychotherapy, showing the superiority of CBT over alternative therapies only among patients with anxiety or depressive disorders. Despite the clear prevalence of empirically-based evidence concerning CBT, the extensive literature also shows the effectiveness of other clinical models. For example, there are the humanistic-experiential therapies that, in Europe, are becoming increasingly widespread, also integrated into approaches not traditionally viewed as humanistic [7] . Some recent reviews observed the effectiveness of humanistic-experiential therapies [8] [9] . Among these clinical models, mainly Emotion-Focused Therapy (EFT) got extensive empirical evaluation that has been considered an Evidence-Based Treatment generating a good deal of research on the process of change, even in children and families [10] . Despite the ever-increasing evidence of their efficacy, humanistic psychotherapies tend to be overlooked in the scientific and health settings [8] .

While a particular area of research highlights the greater effectiveness of certain clinical models, an equally consistent amount of research emphasizes how different approaches can be equally effective. In their review, Cuijpers, van Straten, Andersson and van Oppen [11] observed that there are no major differences in efficacy between the major psychotherapies (CBT, Psychodynamic Problem-Solving Therapy, Interpersonal psychotherapy …) for mild to moderate depression.

The assessment of common factors of the various clinical models has been widely developed in research, and their importance in producing the benefits of psychotherapy has been observed [12] . These commons factors mainly regard process variables—such as empathy, therapeutic alliance, emotion, and interpersonal behaviors—and various studies highlighted how these variables are generally associated with a positive outcome and psychotherapy change [13] [14] [15] [16] . Rihacek and Roubal [17] identified three principal components of psychotherapy change: exploration, acceptance, and understanding of patient experience; attending to patients’ own resources; and providing patients with new skills and advice.

Certain scholars showed the transversal interest in process variables spanning across various clinical models. For instance, regarding the emotional process, Whelton [18] proposed a brief review about it in humanistic, cognitive, behavioral, and psychodynamic psychotherapies, showing the transversal interest in this topic spanning across all therapeutic modalities. In fact, emotional processing and depth of experience are extensively explored both by behaviorists and humanist scholars, who have proven the association with therapeutic outcome and change.

However, as affirmed by Fogarty [4] , the common factors approach fails to account for the specific elements of what works in therapy and “instead, what is needed is an approach that focuses on a treatment modality’s ‘specific factors’” (pg. 46).

Certain scholars have aimed to identify the essential features of the specific clinical model. For instance, Elliott and Greenberg [19] identified five essential features of the Process-Experiential/Emotion-Focused Therapy (PE-EFT). It is a neo-humanistic approach that integrates and updates the five features of Person-centered, Gestalt, and existential therapies.

The pioneer of GT was Perls [20] who, basing his approach on Gestalt psychology (Max Wertheimer and Wolfgang Kohler), put the principles of the human as a total entity into practice. GT is part of humanistic-experiential approach (also including Person-centered therapy, Existential therapy, Psychodrama, Emotion-focused Therapy, Experiential therapy, Transactional analysis, process-experiential therapy) that considers the person as a complex self-organizing system, the growth tendency of human functioning, and the human capacity for reflective consciousness.

In GT literature, certain scholars have attempted to identify the principles and specific features of GT with respect to the clinical approach which it is part of [21] . We proposed a summary of the main features of GT in Table 1.

Thus, the influence of phenomenology and existentialism has been recognized [22] . Phenomenology is the basis of GT as an experiential psychotherapy [23] , as well as the “here and now” experience in the clinical process and therapeutic dialogue [24] .

Albeit GT considers the human being experience lived in the present, it does not neglect the past, which exists in the actual life of people with its unfinished gestalts. As affirmed by Perls [25] , our life is an infinite number of unfinished situations. Such situations are dysfunctional, and in the clinical process the Gestalt therapist helps the patient satisfy his/her need to complete the uncompleted gestalt emerging from the past.

Moreover, GT values the key concept of Self, which is considered a complex and integrated structure that involves a wide range of aspects, also in opposition to one another [26] . While the healthy person recognizes his/her Self formed by such different aspects or even opposite aspects, and accepts the possibility to be

contradictory, the pathological person views him/herself in a one-sided perspective, focusing rigidly on a polarity of the Self [27] . Upon creating a polarity, the split in the personality is at the origin of the person’s discomfort inasmuch as not allowing him/herself to live a complete and holistic experience. GT envisages that the Self exists in interaction with others and it is expressed through the process of human contact: a psychological process in which it is possible to meet one’s self, others, and the environment [28] . GT leads to the recognition of the presence of different contact styles in the individual-environment interactions, some of which functional, creative, or adaptive, and others dysfunctional [28] .

On the other hand, GT is a functionally oriented clinical model [29] , focusing on the importance of the person’s adaptation to a changing environment and the various life situations in an unhindered and healthy way, and to create new responses to new situations (creative adjustments). In fact, as affirmed by Perls et al. [28] the person’s abilities to self-adjust in response to environmental conditions allow his/her growth. This adaptation occurred in terms of figure-ground organization, and while in a healthy patient the figure will emerge clearly from the background and he/she will identify a defined form, in a pathological one the relationship between figure and ground can be inhibited by mental blocks, resulting in an inability to form figures in the here and now.

In the clinical praxis, an important step of GT is the awareness process that does not mean simply developing insight or introspection, but exploring experiences and making sense of our world and our relationship with others and the environment [21] . In fact, a central tenet of the Gestalt clinical method is experimentation, defined as “a behavioral approach for moving to a new way of operating” ( [30] , pg. 31). It is an experiential learning process, based upon what occurs and emerges during the therapeutic encounter, which also involves the use of different techniques (examples are: making aware of unconscious emotional processes; two-chair/empty chair work; working with unfinished situations from the past). In general, through the various Gestalt techniques—which are nothing more than experiments—the therapist allows the patient to transform the tendency to “talk about” into “talk to”, as Perls [25] affirmed. Thus, GT recognizes the importance of a direct impact deriving from representing and “acting” the situation in the present, and it favors the dramatized approach to the experience and conflict-based contents more than the traditional conversational approach [31] .

Moreover, Gestalt therapists believe that in the therapist-patient dialogue the important elements are not only words, but also movements, gestures, tone, and glances, all communicating the relationship between the two. Clemmens [32] sustained that “embodiment is the sensate experience of my body as self in relation to others and the world about me. I know my arms as I reach my heart as I feel it/[myself] beat together, my eyes as I gaze upon the other. Embodiment is a quality of presence, an ontological sense of ‘here and nowness’, and the sense of being awake and fully engaged in the relational world” (pgs. 3-4).

The literature search was based on a comprehensive initiative to set up a database of references to clinical studies investigating the effectiveness of GT, published from 2007 to 2018 in English and Italian.

The literature search strategy involved three steps that are summarized in Figure 1:

1) The first step included systematic searches in the ScienceDirect, PubMed, PsycINFO, and Google Scholar databases. Searches were carried out combining keywords and text relating to GT. For the purposes of the present review, all references related to the search terms Gestalt Therapy, Psychotherapy effectiveness, Psychotherapy approaches, and Clinical models were considered for inclusion. In this first step, we have also included essays that could be useful for a full background of the review topic. We have left out proceedings as they entail a time investment for virtually irrelevant material. Overall, we have viewed 1215 paper titles and abstracts.

2) In the second step, based upon the information provided in the title and abstract, all studies found during the database search were assessed for their relevance to our review. We have applied inclusion and exclusion criteria considering also theoretical or clinical studies useful for a full background of the review

topic. In particular we included papers focusing on GT and on psychotherapy effectiveness regarding also other clinical models. So, we identified 240 papers. The papers met the inclusion criteria, and a full report of the papers was retrieved.

3) In the third step, we added 55 other papers and a total of 295 full texts were examined by only one author, except when the author sought consultation with colleague to examine their centrality to the review’s aims and their quality, proceeding to their further assessment for selection. Any disagreement has been discussed with an additional review researcher. This approach narrowed down the sample to 52 papers, and information from analysis of these full-texts was used as a basis for the review. Among the discarded papers there are also those with no clear findings related to GT and those that did not present an empirical research. Finally, we focused solely on GT effectiveness and a sample of 11 papers was identified for analysis.

To analyze the final sample of 11 papers, we assessed the theoretical basis – as well as the editorial and scientific quality. In particular, we considered papers published in international journals and empirical researches that respected as much as possible a clear and quality procedure. We have excluded summaries at seminars, reports introduced at conferences, dissertations, and comment arts that provided only partial data and authors’ opinions.

A review design, involving three summary sheets, was employed for a straightforward and immediate knowledge concerning the topics background, research’s goal and hypotheses (sheet one), research methods (samples and their main features, cultural context, research design), clinical interventions, procedure and tools utilized (sheet two), and the main findings of the reviewed papers (sheet three). During this phase of quality appraisal, any question and doubt was resolved through a discussion with a colleague and occasionally by enlisting a third reviewer for mediation.

The review synthesis is narrative, because it aims to provide a full picture of the topics and the methods. The various topics emerging from the sample provided a general understanding of the state-of-the-art concerning the review topic and they are summarized in the following discussion sections.

The objectives and methodological features of reviewed papers are resumed in Table 2. In particular, we gathered on research objectives, the sample features and the sampling process, the country in which the research conducted, the research design and procedure, the variables examined and the measured used by the scholars. Then we considered also the therapy method for its importance to observe the different clinical aspects on which the scholars focused. The treatment length also has been examined to assessing the clinical consistent of the treatment proposed.

The majority of researches have been conducted in European (e.g. Serbia, Italy, Spain, Norway), and Extra-European countries (e.g. Mexico, Iran, Australia) and for the most part they used pre-test and post-test research design, which allows to assess the efficacy of clinical treatment or of specific methods and techniques. In some cases, GT was compared with other clinical models. Stevens, Stringfellow, Wakelin and Waring [33] assessed the effectiveness of GT by comparing it to CBT, Person-Centred Therapy, and Psychodynamic Therapy. Arip, Bakar, Ahmad and Jais [34] reported the structure and the content validity of a GT group guidance approach for student self-development, testing its content validity and its applicability in any student experiential context.

The research sample varied depending on the goals. Participants of the therapeutic process were mostly patients with different psychopathologies ( [33] [35] [36] [37] . We have also found samples composed of students [34] and female students with dysthymic disorder [38] or anxious parents [39] , but even offenders [2] , divorced women [40] , participants in group or workshop GT [41] and registered psychiatric nurses trained in GT [42] . In other researches, scholars involved experts [34] , and psychiatrists [42] for the assessment of a GT design and method. In certain researches the sample was composed of few participants, following the principle of qualitative research that favors the deepening and richness of data [42] .

We found poor information concerning sample features and sampling. Generally, scholars reported the participants’ sex and age. In terms of sampling, certain scholars mentioned screening sample criteria such as validated tests [35] and interviews [36] [37] [38] .

Furthermore, the scholars used various selection means. The participants have been engaged by means of advertisement in public media [37] or through organizations and associations [40] [41] .

In terms of the clinical intervention type, researches generally concerned group therapy, sometimes specifying the number of participants, duration, and frequency of the therapy. González-Hidalgo [41] claimed that the workshops were inspired by Naranjo’s psychotherapist training named SAT (Seekers After Truth). Farahzadi and Masafi [38] proposed Gestalt Therapy and Cognitive-Behavioural Play Therapy, and González-Ramírez, et al. [36] used a combination of the Gestalt-Hypnosis Therapy (GHT) and Hypnosis Therapy. Holzinger, et al. [37] combined GT and GT with lucid dreaming.

Certain scholars mentioned group therapy organization. Generally, groups included 7 - 10 participants [2] [35] , which were followed for a set period of time and with sessions of about ninety minutes [37] [40] .

More in particular, the method, used in most proposed clinical interventions, regards different concepts, clinical praxes, and activities referred to GT. The methods we identified are expressive-creative methods, such as drawing [35] , and spiritual/psychological methods, such as meditation, bodywork and movement, or theatre [39] . In some cases, particular activities are proposed such as lucid dreaming [37] , mindful breathing, sensory activity, two-chair work [39] , even the semi-structural individual narrative interview technique to elicit narrative responses from the participants [42] .

In terms of the efficacy assessment of the clinical intervention, we found that various different methods and techniques have been used. Certain researches proposed intervention models involving expert advice, such as the group guidance model proposed by Arip, et al. [34] . González-Hidalgo [41] spent two months as active participant-observers of GT workshops, and Holzinger, et al. [37] used video recordings of sessions during the treatment period. Kelly and Howie [42] employed narrative inquiry, which involves systematic examination of the plots and subplots common to all dreams to identify recurring elements and experiences. Instead, Stevens, et al. [33] assessed the efficacy of GT with a self-report questionnaire (the Clinical Outcomes in Routine Evaluation/CORE), compiled by clients of gestalt therapists who have joined the research project. It is not specifically Gestalt orientated, but it is the most widely used across psychological therapy services in the UK. It includes 34 items which measured subjective well-being, problems or symptoms, life functioning and risk or harm, and it filled in by the client at the beginning and end of their therapy.

The majority of researches aimed to know the outcome effectiveness of GT, especially when it has been applied to group intervention, investigating the important changes that participants reported. The scholars often focused on specific psychopathological, social, and personal issues, as well as on a particular target group. Focusing on the outcomes of GT on indigenous and peasant activists, González-Hidalgo [41] found that GT workshops (conducted following Naranjo’s SAT-HTH training) helped activists both to reflect on their own life stories and to obtain certain advantages in social life. Following the workshops, a number of participants, especially women, gained confidence to participate more actively in community meetings. Such outcome was considered quite remarkable in a society where women are normally absent at community meetings. Exploring GT training efficacy on professional practice, Kelly and Howie [42] reported that psychiatrists recognized the potential application of GT knowledge and skills to their psychiatric nursing practice. Organizing a Gestalt group intervention for anxious parents whose children were studying in primary schools, Leung and Khor [39] found that the clinical approach helped parents to reduce anxiety levels, avoid inner experiences over time, and enhance mindfulness with a slight increase in self-kindness. Focusing on a specific psychological dimension, Saadati and Lashani [40] observed the effectiveness of GT on the improvement of self-efficacy in divorced women that participated in experimental groups. A research paper by Arip et al. [34] reported the overall content validity of the group guidance module in student self-development, based on Gestalt theory and its basic principles (such as holistic approach, person experience, individual responsibility, the here and now method). Applying GT group treatment in prison with a sample of offenders with psychopathology symptoms, Doric [2] found no changes in offenders’ behaviors and lives, although they observed less improvement in depressive groups compared to those suffering of mania, who obtained specific benefits from their active involvement in sessions and from the possibility to resolve basic conflicts in their lives through the analysis of unfinished gestalts.

In a number of papers, the scope of research was to assess the effectiveness of specific Gestalt methods and techniques. Upon undergoing the Gestalt and expressive-creative methods, the geriatric patients analyzed by Drăghici [35] showed certain improvements in their anxious and depressive symptoms, in their global functionality, and in their interactional behavior. In particular, while during treatment, they became aware of the need to resolve their conflicts, even attempting—at the end of the therapeutic process—to obtain the restoration of their confidence, their communication ability, their feelings of group membership, and the awareness that their need for assistance may be fulfilled by means of supportive and relaxation methods. In a paper by Holzinger, et al. [37] , the scholars evaluated the efficiency of lucid dreaming in the treatment of recurring nightmares, observing a significant reduction in nightmare frequency (NMF) at the follow-up and end of therapy phases compared with the baseline. A continuous increase in dream recall frequency (DRF) was observed over three weeks, starting from the 5^th treatment week onward.

Three research papers reported comparisons between GT and other clinical models. So, Stevens, et al. [33] assessed the effectiveness of GT by comparing it to national data bases of similar UK studies about other clinical models, such as Cognitive Behavioural Therapy (CBT), Person-Centred Therapy, and Psychodynamic Therapy. They found that Gestalt Therapy was as effective as other modalities. In fact, the scholars observed that the pre-post treatment difference in their research was comparable to the results observed in studies that analyzed other clinical models, using the CORE method of assessment. Farahzadi and Masafi [38] found the same results upon studying the effectiveness of Gestalt and cognitive-behavioral play therapies to decrease dysthymic disorders and the intensity of symptoms in Iranian children. Instead they observed significant difference in the mean of two clinical models and control group. In particular, the most important feature of both clinical model seems the warm relationship accompanied by confidence-building in the initial sessions. That permitted to children to be able to share their denied feelings (fear, timidity, sadness) and then to express and to talk about these feelings. Focusing on hypnosis, González Ramírez, et al. [36] compared two treatments about it, Hypnosis therapy and Gestalt-hypnosis therapy. They recognized their effectiveness in patients with forms of depression against a control group. While the therapeutic groups showed significant differences between pre-test and post-test results, with an important decreasing in the depression degree, no difference was observed in the control group.