The share of clients who improved fell from 88% after one session to 62% after twelve
In 1,868 primary care clients with planned endings, the improvement rate did not rise with more sessions. It fell, from 88% at one session to 62% at twelve. The likely reason: people leave when they have what they came for.
Suggestive but preliminary. Not settled. how we score evidence
Caveat on this rating: Observational, single country, primary care, twelve sessions at most. Clients chose when to end, so session count is an outcome of improvement as much as a cause of it; that is the paper's own point, and it means the falling percentages cannot be read as later sessions doing harm. The sample was 92.4% White and 73.1% female, as the abstract reports.
If more therapy meant more improvement, the people who attended twelve sessions should have done better than the people who attended one. In this study the opposite was true, and the explanation changed how the field reads its own curves.
Significant findings
Barkham, Connell, Stiles and colleagues followed 1,868 clients seen in routine primary care mental health practices in the United Kingdom. All had planned endings, attended between 1 and 12 sessions, and completed the same outcome measure (the CORE-OM) at the start and end.
The percentage achieving reliable and clinically significant improvement "did not increase with number of sessions attended." Among the 1,472 clients who started above the clinical cut off, the improvement rate "ranged from 88% for clients who attended 1 session down to 62% for clients who attended 12 sessions (r=-.91)."
The authors' reading is the good enough level. Earlier studies had plotted improvement against sessions across everyone and found a curve that rises fast and flattens. This study suggests why: those curves "may reflect progressive ending of treatment by clients who had achieved a good enough level of improvement." People who get what they need leave. The people still attending at session twelve are, on average, the people for whom change is slower.
The other direction
This is not evidence that a twelfth session is useless. It is evidence that the people who needed twelve sessions were different from the people who needed one. The study cannot say what would have happened had the one session clients stayed, or the twelve session clients stopped.
What this does not show
Everyone here had a planned ending and at most twelve sessions. Long term therapy, and people who drop out, are outside the data.
Worth asking
What does ending look like, and can we plan it now?
Source
Dose-effect relations and responsive regulation of treatment duration: the good enough level — Barkham M, Connell J, Stiles WB, Miles JN, Margison F, Evans C, Mellor-Clark J (2006)
Reputable peer-reviewed journal
Read the source: https://doi.org/10.1037/0022-006X.74.1.160
DOI: 10.1037/0022-006X.74.1.160
How this was scored
- Study design
- Cohort study
- Funding
- Funding not disclosed
- Published in
- Reputable peer-reviewed journal
- Sample size
- 1,868
- Preregistered
- not recorded
- Conflicts disclosed
- not recorded
- Independent of proponent
- not recorded
- Retracted
- No
Read the full scoring rubric, including what it can't tell you.
Published September 24, 2026.
Questions
How strong is the evidence behind this?
veisund rates this source "early signal". Suggestive but preliminary. Not settled. It scores 53 out of 100 on our published rubric. One caveat travels with that badge: Observational, single country, primary care, twelve sessions at most. Clients chose when to end, so session count is an outcome of improvement as much as a cause of it; that is the paper's own point, and it means the falling percentages cannot be read as later sessions doing harm. The sample was 92.4% White and 73.1% female, as the abstract reports. The score is calculated from recorded facts about the source — study design, funding, publication venue, sample size, preregistration — not typed in by an editor.
What is the source for this?
Dose-effect relations and responsive regulation of treatment duration: the good enough level — Barkham M, Connell J, Stiles WB, Miles JN, Margison F, Evans C, Mellor-Clark J (2006). Published in: Reputable peer-reviewed journal. DOI: 10.1037/0022-006X.74.1.160. The full source is linked on this page so you can read it yourself.
Who paid for this research, and does that matter?
Study design: Cohort study. Funding: Funding not disclosed. Independence from the proponent is not recorded. Industry sponsorship is one of the most reliably measured biases in medicine, which is why funding carries real weight in the score rather than sitting in a footnote.
Is this medical advice?
This is information to bring to your prescriber, not medical advice and not a reason to change anything on your own. Nothing here is an instruction to stop or reduce a medication. If you are in crisis, call or text 988.
This is information to bring to your prescriber, not medical advice and not a reason to change anything on your own. Nothing here is an instruction to stop or reduce a medication. If you are in crisis, call or text 988.