Review
How much psychotherapy is needed to treat depression? A metaregression analysis

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Abstract

Background

Although psychotherapies are effective in the treatment of adult depression it is not clear how this treatment effect is related to amount, frequency and intensity of therapy.

Methods

To fill this gap in knowledge, the present metaregression analysis examined the association between the effects of psychotherapy for adult depression and several indicators of amount, frequency and intensity of therapy. The analysis included 70 studies (92 comparisons) with 5403 patients, in which individual psychotherapy was compared with a control group (e.g. waiting list, care-as-usual).

Results

There was only a small association between number of therapy sessions and effect size, and this association was no longer significant when the analysis adjusted for other characteristics of the studies. The multivariable analyses also found no significant association with the total contact time or duration of the therapy. However, there was a strong association between number of sessions per week and effect size. An increase from one to two sessions per week increased the effect size with g=0.45, while keeping the total number of treatment sessions constant.

Discussion

More research is needed to establish the robustness of this finding. Based on these findings, it may be advisable to concentrate psychotherapy sessions within a brief time frame.

Introduction

It is well-established that psychological therapies, such as cognitive behavior therapy (Butler et al., 2006), interpersonal psychotherapy (Cuijpers et al., 2011), behavioral activation therapy (Dimidjian et al., 2011), problem-solving therapy (Cuijpers et al., 2007, Malouff et al., 2007), and possibly psychodynamic therapy (Shedler, 2010) are effective in the treatment of adult depression. It is not clear, however, how long such a therapy should last, how many sessions are optimal and what the best intensity of psychotherapy is.

Determining the amount, frequency and intensity of therapy is of great practical and scientific significance. In practical terms, we may draw an analogy here with pharmacological dose-response studies, which seek to discover the optimal dose of a medical substance. If the optimal dose is unknown, chances are that patients will receive either too little or too much medication. Likewise, there probably exists an optimal dose of psychotherapy. If the optimal dose of psychotherapy is low, then a few brief sessions may suffice to combat depression. Such brief treatments may greatly reduce the personal and societal burdens of depression (Kazdin and Blase, 2011). On the other hand, if the optimal dose of psychotherapy is high, then it becomes sensible for society to invest in extended treatments, because these translate directly into greater health benefits. At a scientific level, gaining insight into the optimal number of treatment sessions can illuminate the change process in patients and improve the theoretical understanding of how psychotherapies support this process.

Early research in psychotherapy has suggested that the improvement in patients increases with a larger number of sessions (Howard et al., 1986, Kopta et al., 1994). A systematic review found that about 60% of patients had improved after about 13 sessions (Hansen et al., 2002). In this research, it is usually assumed that the effect of therapy is greater in earlier sessions and levels off as the number of sessions increases (Kopta et al., 1994). There is, however, also evidence suggesting that the effects of increasing the number of sessions differ depending on the characteristics of the problem and the therapy (Barkham et al., 2006, Reynolds et al., 1996). Pooling the outcomes for several groups of patients and therapies may artificially create the impression of diminishing returns for later sessions, which in actuality are based on a set of multiple linear improvements. Most research on the influence of number of sessions on outcome, however, is based on open, uncontrolled studies (Hansen et al., 2002, Hansen and Lambert, 2003). These studies do not account for natural recovery rates and consequently these studies can only show that patients get better during treatment. Whether this improvement can be attributed to the treatment cannot be established with uncontrolled studies.

Trials in which longer and shorter therapies are directly compared with each other in randomized trials, can much better answer the question whether longer therapies are more effective than brief therapies. In the field of psychotherapy for adult depression, three such trials have been conducted (Shapiro et al., 1994, Barkham et al., 1996, Dekker et al., 2005). The results of these studies have been mixed. Some studies found larger effects for longer therapies, especially in more severe depression (Shapiro et al., 1994, Barkham et al., 1996). However, other studies found no or limited differential effects of longer versus shorter therapies (Dekker et al., 2005, Molenaar et al., 2011).

It is further important to note that not only the number of sessions is relevant when examining the association between amount, frequency and intensity of therapy on the one hand and outcome on the other. The duration of a session typically varies from half an hour to 2 h, resulting in considerable differences in total time of contact between client and therapist. Moreover, the frequency of therapy session can also vary considerably, with some therapies having two sessions per week, while others have only one session per two weeks. This results in considerable differences in the total duration and intensity of psychotherapy. There is very little knowledge about these indicators and their association with the effects of psychotherapies for depression.

There is some evidence from the field of anxiety disorders on these issues. In one randomized trial it was found that 12-weekly sessions of cognitive behavior therapy resulted in better outcomes and less drop-out than the same number of sessions extended over 18 weeks (Herbert et al., 2004). Another trial found that a massed three-week cognitive behavioral therapy for panic disorder was equally effective as a traditional spaced 13-week cognitive behavioral therapy schedule (Bohni et al., 2009). Abramowitz et al. (2003) examined whether 15 sessions of therapy delivered daily over 3 weeks was more effective than the same 15 sessions delivered twice weekly over 8 weeks, and found a trend toward more improvement in the intensive group. We found no trial of this kind in the field of psychotherapy for depression, however.

In view of these important gaps in the literature, we decided to conduct a meta-analytic study that systematically examined the association between effectiveness of psychotherapies for adult depression on the one hand and the number of treatment sessions, duration and frequency on the other. Our meta-analysis sought to improve prior research in this domain in two main ways. First, unlike previous work, we focused on randomized controlled trials, which afford greater confidence in the causal effects of psychotherapy. Second, we examined the association between the effects of psychotherapies for adult depression and several indicators, namely: numbers of treatment sessions, duration of treatment, total contact time with the therapist, and the number of sessions per week. To the best of our knowledge, no meta-analysis has examined these indicators before in the field of psychotherapy for adult depression.

Section snippets

Identification and selection of studies

We used a database of 1344 papers on the psychological treatment of depression that has been described in detail elsewhere (Cuijpers et al., 2008b), and that has been used in a series of earlier published meta-analyses (www.evidencebasedpsychotherapies.org). This database is continuously updated through comprehensive literature searches (from 1966 to January 2012). In these searches we examined 13,407 abstracts in Pubmed (3320 abstracts), PsycInfo (2710), Embase (4389) and the Cochrane Central

Selection and inclusion of studies

After examining a total of 13,407 abstracts (9860 after removal of duplicates), we retrieved 1344 full-text papers for further consideration. We excluded 1274 of the retrieved papers. The reasons for excluding studies are given in Fig. 1. This resulted in a total of 315 randomized psychotherapy trials on adult depression. Seventy trials examined the effects of individual psychotherapy and met all other inclusion criteria. Fig. 1 presents a flowchart describing the inclusion process.

Characteristics of included studies

Seventy

Discussion

In the present study, we examined the association of the effects of psychotherapy for adult depression and multiple indicators of amount, frequency and intensity of therapy. We found that the effects increased somewhat with a higher number of treatment sessions. However, this association was not very strong, with ten more session resulting in an increase of the effect size with 0.1. This is a very small effect (Cohen, 1988) and it can be questioned whether this has any clinical relevance.

Role of funding source

No fund was received for this study.

Conflict of interest

None.

Acknowledgments

None.

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