The dose-response effect in routinely delivered psychological therapies: A systematic review

Abstract

The dose-response effect refers to the relationship between the dose (e.g., length, frequency) of treatment and the subsequent probability of improvement. This systematic review aimed to synthesise the literature on the dose-response effect in routine psychological therapies delivered to adult patients with mental health problems. Twenty-six studies were eligible for inclusion. Different methodological approaches have been used to examine the dose-response effect; including survival analysis, multilevel modelling and descriptive cluster analyses.Replicated and consistent support was found for a curvilinear (log-linear or cubic) relationship between treatment length and outcomes, with few exceptions such as eating disorders and severe psychiatric populations. Optimal doses of psychotherapy in routine settings range between 4 -26 sessions (4 -6 for low intensity guided self-help) and vary according to setting, clinical population and outcome measures. Weekly therapy appears to accelerate the rate of improvement compared to less frequent schedules. Most of the reviewed evidence is from university counselling centres and outpatient psychotherapy clinics for common mental health problems. There is scarce and inconclusive evidence in clinical samples with chronic and severe mental disorders.

Dose‐response patterns in low and high intensity cognitive behavioral therapy for common mental health problems

“…Conversely, extending therapy beyond these dose‐response intervals (up to 24 sessions; Robinson, Delgadillo, & Kellett, 2020) is warranted for patients who have shown signs of RCSI, and we strongly caution against the arbitrary restriction of treatment sessions for these cases. Prior research has shown that IAPT services that offer a low mean number of treatment sessions tend to attain poorer clinical outcomes (Clark et al, 2018), and therefore offering an adequate dose of therapy is central to effective and ethical practice (National Collaborating Centre for Mental Health, 2018).…”

“…First, compared to IAPT recovery rates which classify cases based on symptomatic reductions below the cut‐offs for PHQ‐9 and GAD‐7 (National Collaborating Centre for Mental Health, 2018), the strict RCSI criteria applied in this study additionally requires the observation of statistically reliable improvement and therefore yields more conservative estimates of treatment response. As shown in a methodological review on this topic (Robinson, Delgadillo, & Kellett, 2020), studies that use RCSI criteria (rather than more lenient indices of improvement) tend to yield lengthier dose‐response parameters which are less likely to classify cases that take longer to benefit from therapy as nonresponders. Second, we report RCSI rates separately for low and high intensity interventions, whereas IAPT recovery rates reflect improvements observed during the whole stepped care treatment pathway starting with an initial (pretreatment) assessment.…”

“…A systematic review of dose‐response studies found that adequate dose recommendations varied according to clinical populations and methodological approach (Robinson, Delgadillo, & Kellett, 2020). For example, patients with psychosis required 8–30 sessions of high‐intensity cognitive‐behavioral therapy (CBT) (Falkenström, Josefsson, Berggren, & Holmqvist, 2016; Lincoln, Jung, Weisjahn, & Schlier, 2016), while patients with mild‐to‐moderate anxiety and depression required only 4–6 sessions of low‐intensity CBT (Delgadillo et al, 2014; Delgadillo, Kellett et al, 2016).…”

“…Furthermore, studies using more or less conservative definitions of treatment response yield different conclusions (Anderson & Lambert, 2001; Asay, Lambert, Gregersen, & Goates, 2002). Overall, it is evident that adequate dose parameters need to be calibrated in diagnostically homogenous groups, in large and adequately powered samples, using stringent definitions of treatment response (Robinson, Delgadillo, & Kellett, 2020).…”

The influence of socio-demographic similarity and difference on adequate attendance of group psychoeducational cognitive behavioural therapy

“…A number of replicated findings in different studies indicate that the optimal dose of low intensity CBT interventions is between 4 and 6 sessions (Delgadillo et al, 2014, Delgadillo, Kellett, et al, 2016Firth et al, 2015). A recent systematic review of this literature concluded that the probability of symptomatic remission is minimal in cases that access less than 4 sessions of low intensity CBT interventions (guided self-help), thus offering an evidence-based criterion to define adequate attendance (Robinson, Delgadillo, & Kellett, 2019). We considered that attendance of all 6 sessions was too strict a criterion to denote adequate engagement with SC, since it is common that patients miss one or two sessions due to practical obstacles such as work or childcare commitments, so our definition of adequate attendance is in line with the current evidence-base for the minimum recommended number of sessions for low intensity CBT (Robinson et al, 2019).…”