Global impact of depression
Depression is a common problem, affecting about 121 million people world‐wide. Depressive disorder is characterised by a marked lowering of self‐esteem and feelings of worthlessness and guilt. A persistent low mood leads to changes in appetite, sleep pattern and overall functioning. Symptoms further include anhedonia, fatigue and impaired concentration. (ICD 10) At its worst, depression can lead to suicide, which is associated with the loss of 1 million lives per year. Depression is projected to become the leading cause of disability and the second leading contributor to the global burden of disease by the year 2020. It occurs in persons of all genders, ages, and backgrounds (WHO 2001). The huge personal and economic impact of depression implies a need for systematic reviews of the evidence for efficacy for all current treatment modalities.

Treatments for depression
Depression is widely assumed to be effectively treated with a combination of pharmacological and talking therapies. Both tricyclic antidepressants and the more recent selective serotonin reuptake inhibitors (SSRIs) have been found to be effective in treating depression (Paykel 1992; Edwards 1992). However, in a recent Cochrane Review, Moncrieff 2003 found small differences between anti‐depressant medications and active placebos with the lowest effects found in inpatient trials. A variety of talking therapies have also been found to be helpful in treating depression and two systematic reviews are currently in progress comparing psychological and pharmacological treatments (Churchill 2003 a; Churchill 2003 b).

Depression is also one of the most common reasons for the use of complementary and alternative therapies (Ernst 1998). The reasons for this are complex and vary according to client group. They may entail a lack of satisfaction with conventional treatments, and/or a wish to avoid side‐effects from medication or the stigma attached to seeking talking therapy. In the case of music therapy, people may feel more able to access this medium as listening to or playing music in other contexts has been felt by the individual to be beneficial. Music therapy might also be indicated for populations who have difficulties in using words, such as those with a learning or physical disability. Music therapy might also be used where non‐directive talking therapies are considered inappropriate, for example where depression is secondary to a psychotic illness or severe personality disorder.

Music therapy
Although music has been used for the purpose of improving health throughout the history of mankind (Horden 2000), it was not until the middle of the 20th century that music therapy was developed and instituted as a clinical method. Music therapy began to be used by US government programmes in the 1940s, and in Europe two decades later (Bunt 1994). It is now a state registered profession in some countries (UK and USA) and is used extensively in many types of treatment and rehabilitation facilities from psychiatric hospitals to hospices to private practices on all continents (Maranto 1993). Music therapy has been defined as "a systematic process of intervention wherein the therapist helps the client to promote health, using musical experiences and the relationships that develop through them as dynamic forces of change."

Music therapy models are based on different theoretical backgrounds, such as psychodynamic, humanistic, and behavioural, but also educational theories. The techniques used in music therapy can be broadly classified as Active, when clients re‐create, improvise or compose music, and Receptive, when clients listen to music. (Bruscia 1998). Often, a combination of different techniques is used in the same therapy. The choice of approach tends to be based upon the client's needs, the therapist's training and the context (Drieschner 2001; Wigram 2002).

In most approaches, clinical music therapy offers a therapeutic relationship in which the client can experience himself differently either by making music or by listening to it with the therapist. In Active approaches, the therapist is a trained musician and uses clinical improvisation techniques to stimulate or guide or respond to the client who may use his/her voice or any musical instrument of choice within his/her capability (such as marimba, gong, cymbal, drums, guitar, harp, piano). Clients may also bring songs written by them or others, or pre‐composed music to play with the therapist. Active forms of music therapy also aim to offer the client a way of experiencing and exploring new ways of relating.

Receptive forms frequently involve an adjunctive activity performed whilst listening to live or recorded music, such as relaxation, meditation, movement, drawing, reminiscing etc. Aims in this sort of music therapy might include reducing stress, soothing pain, or energising the body. In a psychodynamic approach, listening to songs might help access feelings which the client can then work through verbally. For older adults, it might facilitate structured reminiscence or life review (Bruscia 1991).

Music therapy can be carried out in the long‐term (for example more than 3 years), medium term or short term. Intensity of treatment also varies from daily to weekly to monthly treatment. Patients might be seen in groups or individually, they may drop in to an open group (for example in a psychiatric ward setting) or have been referred and assessed by the music therapist before being placed in individual treatment or a closed group. Music therapy may be carried out by a trained therapist or a trainee therapist on placement. There are still a number of untrained practitioners who call their practice music therapy, and due to the relative newness of music therapy as a profession and the lack of evidence available, these will be included in this review. To be classified as well‐defined music therapy, there should also be a coherent theoretical framework underpinning the intervention.

Need for a review of the evidence
Proponents of music therapy have suggested that it may be particularly beneficial for people who experience mental distress (e.g. Hadsell 1974; Benenzon 1981). For example, one observational study concluded that music therapy may have beneficial effects for people experiencing depression (Reinhardt 1982), a finding which was subsequently supported by a small randomised control trial of music therapy vs waiting list control among older adults with depressive disorders (Hanser 1994). However, a preliminary scan of the few systematic attempts at experimental research in this field highlights a number of difficulties. In particular, all RCTs have suffered from small sample sizes, making outcomes difficult to gauge accurately. In addition, client groups are often heterogeneous (Radulovic 1997) and as mentioned above, types of music therapy vary enormously. However, as music therapy is being sought and accessed for the treatment of depression as a complement or alternative to pharmacological or other psychological therapies, there is a need for a systematic review of the evidence available to support its use with this client group.

There is also a case for comparing different music therapy approaches although this is difficult given the overlap of techniques used in all approaches. This is justified where the treatments are strikingly opposing, for example if we were to compare long‐term individual psychotherapeutic improvisation and short‐term large‐group exercising to music.