This review concluded that supervision appeared to have a positive impact on a number of outcomes for psychotherapists, counsellors and, to some extent, their clients. However, in the majority of cases, the studies lacked methodological rigor and had varying characteristics, suggesting that the authors' findings should be interpreted with caution.

To assess the impact of clinical supervision on psychotherapists and counsellors, their clients and practice.

ERIC, PsycINFO, MEDLINE, EMBASE, WorldCat Dissertations, International Bibliography of the Social Sciences (IBSS) and the Cochrane Library were searched from 2002 to early 2006. Search terms were reported. A search strategy was used as the main source of articles prior to 2002. All relevant published or unpublished studies written in English, from 1980 to 2006, were included. In addition, relevant journals were handsearched and the reference lists of books on supervision were screened.

Empirical studies (quantitative and qualitative) assessing the effects of clinical supervision on the work of counsellors, psychotherapists and other trained professionals, with real clients, were eligible for inclusion in the review. The following studies were excluded from the review: studies of family therapy; studies which did not include a valid and reliable outcome instrument or a rigorous qualitative analysis; studies using self-reported satisfaction with supervision; studies of psychiatrists, psychiatric nurses, occupational therapists and other health professionals having supervision; studies of role-play sessions; studies of one-to-one peer supervision or peer group supervision; and discursive articles and case studies. Online and telephone supervision studies were only included if they met all other inclusion criteria. Group supervision studies were only included if data related to therapeutic work with individuals or couples.

The majority of included studies were carried out in the USA. Participants in the included studies were mainly trainees, aged 22 to 54 years old. Included interventions were categorised as having an impact on self-awareness, skills, self-efficacy, timing and frequency of supervision, theoretical orientation, support and outcome for the client. A range of outcome tools were used.

One reviewer assessed all of the abstracts for inclusion. Any ambiguous abstracts were either further assessed by two reviewers or an assessment was made based on the full paper.

Studies were rated on a scale of 1 to 5 based on their methodological rigor (1=not at all and 5=excellent) and their overall quality (1=very poor and 5=very good). Validity criteria included: allocation of control groups; study biases; study limitations; sample procedures; factors favourable to developing and delivering the intervention; and the relevance of findings to the future development of supervision interventions.

The authors were not explicit about how the validity assessment was performed.

Two independent reviewers extracted data and summarised the main findings from half of the included studies. This data was cross-checked. Any missing data or discrepancies were corrected by the two principal reviewers. The remaining data was extracted by a single reviewer and were not cross-checked.

A narrative summary was presented, which grouped studies by intervention type.

Eighteen studies (number of supervisees ranged from one to 274) were included in the review. Eight studies were quantitative. Three studies were qualitative. Seven studies used mixed methods. Quality scores ranged from 2 (poor) to 5 (very good), with most studies rated as average and only two studies rated as "very good".

Two qualitative studies of average quality reported that self-awareness was enhanced by supervision.

Four average quality studies and one very good quality study suggested that both individual and group supervision was associated with a range of improved counselling skills.

One poor quality study, three average quality studies and one very good quality study reported positive effects in counsellors' self-efficacy. One average quality study also assessed whether self-efficacy increased as working alliances became stronger, but found no evidence to support this.

One average quality and one poor quality study suggested that the timing and amount of supervision affected the process and outcome of supervision.

Two average quality studies reported that awareness, development and changes in theoretical orientation reflected the supervisees' ongoing development.

One poor quality study found support to be beneficial. Two average quality studies and one poor quality study found mixed effects for support on client outcomes.

Supervision appeared to have a positive impact on therapist self-awareness, skills, self-efficacy, theoretical orientation, support and to some extent outcomes for clients, but the quality of the data was variable.

This review was based on a clear, but broad research question. A number of literature sources were searched for both published and unpublished data. Studies may have been missed through the inclusion of only English language studies published from 1980. Some attempts were made to reduce the risk of reviewer error and bias, through the independent verification of decisions and data. However, such precautions were not always fully applied and, in some cases, it was unclear whether they were applied at all. The quality of the studies was assessed and taken into account when formulating the overall findings. However, in the majority of cases, the studies lacked methodological rigor and varied considerably in their characteristics, suggesting that the authors' findings should be interpreted with caution.

Practice: The authors stated that the usefulness of the review findings to practice is mixed and, although supervision appears to offer opportunities to improve practice and gain confidence, evidence to support improved client outcomes is tentative.

Research: The authors stated that there is a need to carry out more well-designed randomised controlled trials of supervision, as well as rigorously conducted qualitative research including case-studies. Studies are required to investigate the performance of counsellors and therapists from the perspective of client outcomes, and to investigate the effects of supervisor variables and their impact on therapists and clients.

British Association for Counselling and Psychotherapy.

Wheeler A. Research on supervision of counsellors and psychotherapists: a systematic scoping search. Rugby: BACP; 2003.

Wheeler S, Richards K. The impact of clinical supervision on counsellors and therapists, their practice and their clients: a systematic review of the literature. Rugby: BACP; 2007.

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.