Research on prevention differentiates between universal interventions, which are implemented for a designated population regardless of the risk (e.g., all school-age children) and targeted interventions, which are aimed at a population at high risk for a disorder. Recent large trials in adults covered on the Mental Elf showed prevention of depression is particularly effective when it is targeted.
In a recent Cochrane systematic review, Hetrick and colleagues examined whether three evidence-based psychological interventions (cognitive behavioural therapy (CBT), interpersonal therapy (IPT) and ‘third wave’ CBT) are effective in preventing the onset of depressive disorder in children and adolescents.
The authors included randomised controlled trials (RCTs) on both universal and targeted interventions for children and adolescents whose mean age ranged between 5 and 19.9 years. Studies were included if participants did not currently meet the criteria for a diagnosis of depressive disorder. However, participants with a history of depression were included if the intervention was directed at preventing depression in a non-clinical setting and participants were not being currently treated for depression. The authors argue that while this might come across as a more flexible definition of prevention, the majority of included trials did not assess whether participants did in fact have a history of depression.
- Eligible interventions were either CBT (including problem-solving interventions and third wave approaches), or IPT-oriented
- Comparison groups could include treatment as usual (TAU), no treatment (NT), waitlist (WL) or attention placebo (AP), defined primary by comparing for non-specific factors.
All outcomes were assessed at four time points:
- Short-term follow-up (up to 3 months)
- Medium-term follow-up (4-12 months), and
- Long-term follow-up (over 12 months).
Primary outcome measures included:
- Prevalence of depression diagnosis at medium-term follow-up (between four and 12 months), measured according to a recognised diagnostic system.
- Depression symptoms at post-intervention assessed using a standardized, validated self-report measure.
Secondary outcomes included:
- Depression diagnosis and symptoms at other time points (self-reported and clinician-rated)
- Anxiety symptoms, and
- General and social functioning at post-test and follow-up.
Treatment effect was quantified primarily by the risk difference (RD) and its corresponding 95% confidence interval (CI), as the main question was whether the onset of an episode of depressive disorder was lower following an intervention; that is if the absolute number of participants receiving a diagnosis following the intervention was lower than their number in the control group. For continuous outcomes, the authors computed the standardized mean difference (SMD) and corresponding 95% CIs.
- 83 trials were included, most of which (52) included a simple randomiSation procedure whereby participants were allocated to an intervention or control group. The remaining studies were cluster trials (where the schools, classes or families, rather than the individual were the unit of randomisation).
- The majority of trials (67) were conducted in school settings. Twenty-nine trials were addressed to unselected populations (universal prevention), and 53 in targeted populations.
- For the primary outcome of depression diagnosis at medium term follow-up, 32 trials resulted in a small significant effect of the intervention in reducing the risk of a diagnosis as compared to a control group (RD -0.03, 95% CI -0.05 to -0.01). This translated into a number needed to treat to benefit of 33. However, there was no evidence of an effect at short-term or long-term follow-up. The authors rated this a moderate-quality evidence. There were no differences in efficacy between targeted and universal prevention intervention, with the exception of short-term assessment, where the former showed a higher efficacy.
- For the primary outcome of self-rated depression symptoms at post-intervention, there was a small but statistically significant benefit of prevention interventions (SMD -0.21, 95% CI -0.27 to -0.15). This effect was preserved at the short- and medium-term assessment points, but not at long-term follow-up. The authors rated this as low- to moderate-quality evidence. Targeted interventions were more effective than universal ones (P = 0.001) only at medium-term follow-up.
- For the secondary outcome of anxiety, there was a small effect of prevention programmes at short- and medium-term (SMD= -0.08, 95%CI -0.14 to -0.01), but not at post-intervention or long-term.
- There was a dearth of attention placebo-controlled trials in targeted prevention interventions. However, for trials focused on universal prevention, comparison with attention placebo controls consistently showed no effect.
- There was no evidence of publication bias for the primary outcome measures, a finding that the authors attribute to their exhaustive search procedure and extensive contact with a large number of trial authors.
The authors conclude that:
Overall the results show small positive benefits of depression prevention, for both the primary outcomes of self-rated depressive symptoms post-intervention and depression diagnosis up to 12 months (but not beyond). Estimates of numbers needed to treat to benefit (NNTB = 11) compare well with other public health interventions.
They also add that:
Prevention programmes delivered to universal populations showed a sobering lack of effect when compared with an attention placebo control.
Strengths and limitations
As already noted, the authors used an exhaustive search procedure, chose a relevant primary outcome for prevention research, conducted appropriate sensitivity and moderation analysis and transparently reported their findings.
However, there are some limitations:
- I am not sure why the authors focused exclusively on CBT (including third wave CBT), IPT and their combination. The authors argue previous reviews of prevention of depression in this population revealed most interventions were CBT or IPT, and also that these interventions have the most robust evidence for the treatment of depression. However, they do not present separate comparisons for CBT or IPT and hence this restriction appears somewhat arbitrary, particularly given ‘third wave’ CBT interventions are nonetheless included, even if evidence for them in this particular population is limited.
- The quality of the evidence was problematic for the potential sources of bias. Notably, over half of the trials were rated as having high or unclear risk of bias for incomplete outcome reporting, a domain assessing whether all randomised participants were included in the analysis. Only a quarter of the trials had registered protocols available and out of these only eight could be rated as having a low risk of bias due to selective outcome reporting, a bias domain checking whether outcomes presented in the protocol fully match those reported in the paper.
- For many of the secondary outcome variables, results were based on a very small number of trials, particularly at some time-points (in some cases just one or two trials contributed to the effect). This renders many of these results potentially unreliable.
- While for prevention interventions longer term effects are certainly the most relevant, the separation into post-intervention, short-, medium- and long-term is somewhat confusing and difficult to interpret, particularly for some categories of outcomes where the authors get significant results for some of the time points considered but not for others.
- Looking at the change in depressive symptoms or in other such symptom outcomes is of little relevance for universal prevention interventions and hence combining these with targeted prevention could be misleading for these outcome categories.
Interventions to prevent depression in children and adolescents have a small effect in reducing the risk of obtaining a diagnosis of depression until up to 12 months following the intervention, but not beyond that. The evidence is insufficient to support the implementation of depression prevention programs in this population.
Hetrick SE, Cox GR, Witt KG, Bir JJ, Merry SN. Cognitive behavioural therapy (CBT), third-wave CBT and interpersonal therapy (IPT) based interventions for preventing depression in children and adolescents. Cochrane Database of Systematic Reviews 2016, Issue 8. Art. No.: CD003380. DOI: 10.1002/14651858.CD003380.pub4.