Introduction

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Depressive disorders are a common problem in child psychiatric clinics.¹ These common disorders are associated with a range of adverse outcomes, including severe social impairment, long term effects on cognitive development, suicidal behaviour, and a high risk of recurrence.² There is much literature reviewing the usefulness of tricyclic medication in childhood depression, but a systematic review found tricyclics to be of uncertain benefit.³ The results of randomised studies of selective serotonin reuptake inhibitors have been contradictory, with one positive⁴ and one negative result.⁵

There has therefore been a growing interest in psychological treatments, particularly in cognitive behaviour therapy. The results of trials of cognitive behaviour therapy in depressed young people have, however, been difficult to interpret. Although some trials have found significant benefits, the numbers have been small and the confidence intervals for the rate of improvement have been wide. In addition, the quality of the studies varied greatly. We therefore submitted the existing literature to a systematic review. We pooled the results of randomised trials to see whether cognitive behaviour therapy is superior to other conditions in the treatment of childhood and adolescent depressive disorders. We also examined whether the results were materially influenced by the quality of the reported studies.

	Methods

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Definitions and inclusion criteria
The systematic review was restricted to studies in which one of the therapies was a recognised form of cognitive behaviour therapy as described in standard textbooks on the subject. ^{6 7} Studies of family therapy ^{8 9} or interpersonal psychotherapy¹⁰ were excluded.

Search methods
The search was conducted in stages. In the first stage, conducted by RH, the literature was searched with Medline (1966-97) and Psych-lit. Reference lists from reviews and book chapters were searched, and conference proceedings were reviewed. This stage suggested that there were probably enough studies suitable for inclusion in a quantitative analysis.¹⁵ In the second stage, conducted independently by JW and PS, the computer searches were repeated and all journals that had published a randomised controlled trial in this field were searched manually. When relevant, authors of published papers were approached for further details of their work. Investigators working in the specialty were contacted. The Cochrane library was also searched for randomised trials.

Search results
The search identified 22 potential comparative studies in which cognitive behaviour therapies had been used with depressed young people. Four studies were excluded because assignment to treatment was not random,^16-19 one because it was an interim analysis of an ongoing study,²⁰ and 11 because they involved children with depressive symptoms and not depressive disorder.^21-31 This left six randomised trials of cognitive behaviour therapy for depressive disorder in young people.^32-37 Two of the trials were conducted by the same research group ^{32 34} but it was clear from the trial descriptions that they were based on different samples. We did not find any studies that compared cognitive behaviour therapy with medication.

Quality assessment
Quality of the studies was assessed by using a modified version of the scheme used by Hazell and coworkers in their systematic review of the tricyclic studies.³ Their scheme was based on the method of Chalmers and colleagues.³⁸ The cognitive behaviour therapy studies were rated independently by JW and PS and disagreements were resolved by consensus. Each of 12 features of a study was rated on a 0-3 scale, making a total possible score of 36. These features were:

• Quality of description of randomisation
• Inclusion of data on subjects who subsequently withdrew from the study (intention to treat)
• Degree to which the assessors were blind to the allocated treatment
• Degree to which the expectancy of subjects about treatment was assessed
• Clarity of description of improvement
• Use of multiple informants to assess outcome
• Whether the therapy was specified in a manual and the degree to which the adherence of therapists to the manual was checked
• Degree to which compliance with the therapy was assessed
• Whether concurrent treatment was held constant
• Length of baseline assessment
• Control for previous treatment
• Control for comorbidity

Outcome measurement
In all studies depressive disorder was diagnosed with operational criteria.¹⁴ Five of the six studies used the same standardised interview to establish whether these criteria were met (Puig-Antich J, Chambers W, Schedule for affective disorders and schizophrenia for school aged children, available from New York State Psychiatric Institute). In the sixth the clinician made a global judgment on the basis of an interview and the subject's responses on standardised depression questionnaires.³³ Only two studies have thus far reported follow up data, ^{35 39} and this meta-analysis was therefore restricted to outcomes immediately after treatment. The outcome was remission from depressive disorder.

Statistical analysis
For each study we estimated the ratio of the odds of remission after cognitive behaviour therapy compared with the odds in the comparison group or groups. Confidence intervals were calculated with the Logit approximation. The pooled odds ratio was estimated with the DerSimonian Laird method,⁴⁰ with a random effects model. A test of heterogeneity was performed.

	Results

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Table 1 summarises descriptive information on the studies. No study included inpatients. Cognitive behaviour therapy was compared with a heterogeneous set of comparison interventions. Most of these interventions were designed either to be inactive (such as waiting list) or to be an attention placebo (for example, relaxation training, art exercises).

Per protocol analysis
Table 2 shows the numbers without depressive disorder at the end of treatment. All studies showed positive effects in favour of cognitive behaviour therapy. In three studies the 95% confidence intervals for the odds ratio did not include 1 (figure), indicating a significant difference in favour of cognitive behaviour therapy over the comparison conditions (129/208 v 61/168). There was no significant heterogeneity across the sample (²=4.5; df=5; P=0.47). The pooled odds ratio was 3.2 (95% confidence interval 1.9 to 5.2), suggesting significant improvement in the cognitive behaviour therapy group over the comparison group.

View larger version (16K): [in this window] [in a new window]   Efficacy of cognitive behavioural therapy in childhood and adolescent depressive disorder. Cochrane odds ratio plot (random effects model)

Intention to treat analysis
The per protocol analysis ignored withdrawals from treatment (table 2) and may therefore have exaggerated the effects of cognitive behaviour therapy. To obtain a more conservative estimate of the effect of implementing therapy we conducted an intention to treat analysis in which we assumed that all withdrawals in the cognitive behaviour therapy group did not remit and all withdrawals in the control groups remitted (that is, remission rates of 129/218 and 75/182, respectively). The pooled odds ratio was 2.2 (1.4 to 3.5).

Study quality
The mean quality rating of the cognitive behaviour therapy studies was 22.7. This is similar to that in the tricyclic studies,³ in which the mean for the five studies that presented data on remission was 23.8. There was a small negative association between the quality rating and the odds ratio (rank r=0.46; P>0.10). This was largely because the two trials with lower scores on the quality scale showed the strongest treatment effects (tables 1 and 2). The effect of cognitive behaviour therapy was still found to be significant when these trials were excluded, with remission rates in an intention to treat analysis of 105/161 in the cognitive behaviour therapy group and 69/152 in the comparison conditions. This gave an odds ratio of 2.2 (1.3 to 3.5).

	Discussion

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The treatment of depressive disorders is an important clinical issue for child mental health teams yet little is known about the best ways of helping these children. A systematic review of the tricyclic studies suggested that tricyclics were of uncertain benefit.³ The present systematic review of cognitive behaviour therapy studies seems to show that it is a useful treatment for children and adolescents with depressive disorders. Several issues need to be borne in mind, however, in the interpretation of these results.

Potential biases
With only six small trials it is difficult to use techniques such as funnel plots to examine the possibility of bias. Nevertheless, the absence of studies with a negative odds ratio does raise this possibility because it would be expected that even when a treatment is effective some small trials would have negative results.⁴¹

Clinical heterogeneity
There was no statistical evidence of heterogeneity in this meta-analysis, but power to detect heterogeneity was low because of the small number of available trials. It is likely, however, that there was some clinical heterogeneity. In three of the trials factors that predict outcome were analysed within the studies. These analyses all showed that greater severity of depression was a significant predictor of failure to remit after cognitive behaviour therapy (DA Brent et al, personal communication). ^{42 43} The implication is that cognitive behaviour therapy may be most effective for depression of moderate severity.

Spontaneous improvement
The high rate of improvement among children in the comparison group also requires some comment. The comparison group consisted mainly of interventions that were designed either to be inactive or to be an attention placebo. Only one study included an active comparison interventionfamily therapy.³⁷ The finding that more than a third of depressed patients improved with these inactive interventions suggests that there is a high rate of spontaneous remission in moderately severe juvenile depression. Cognitive behaviour therapy is an expensive intervention, taking up to 16 sessions in some of the studies reviewed here. There is a strong case then for using a brief supportive intervention as the first line treatment and reserving cognitive behaviour therapy for patients who fail to respond.

Conclusions
This systematic review suggests that cognitive behaviour therapy may be of benefit for mild or moderate depressive disorder in young people. It was based on only six trials, however, many of which were relatively small. Definitive larger trials will therefore be required to establish whether the results of the present meta-analysis are reliable. In the meantime, the available data suggest that cognitive behaviour therapy is a promising treatment for depressed young people.