Across 114,123 patients, how long therapy lasted did not predict how people ended up
A preregistered meta-analysis of 15 studies found no overall link between treatment length and outcome (r = -0.24, p = .27). Longer treatments went to people who started worse and changed more slowly.
Reasonable evidence with real limitations. how we score evidence
Caveat on this rating: A meta-analysis of observational routine-care studies, so the null association is descriptive, not causal. The confidence interval on the main estimate is wide (-0.70 to 0.36), which is consistent with a moderate association in either direction as well as with none. The authors themselves say results depended on the methodological criteria applied.
The good enough level began as one study's explanation for a curve. By 2021 there were enough studies to test it across more than a hundred thousand people.
Significant findings
Bone, Delgadillo and Barkham ran a systematic review and meta-analysis, preregistered on PROSPERO, of every study that stratified therapy clients by how long their treatment lasted. Fifteen studies were synthesised, with 114,123 people in total; ten of them fed two meta-analyses (n = 46,921 and n = 41,515).
"In support of the GEL, there was no overall association between treatment duration and outcomes (r = -0.24, 95% confidence interval [CI: -0.70, 0.36], p = .27)."
Who stayed longer was not random. "Longer treatments were associated with higher baseline symptom scores (r = 0.15, 95% CI [0.08, 0.22], p < .001) and slower rates of change." Shorter treatments more often showed a curve that flattened; longer treatments more often showed steady, linear change.
The other direction
The authors do not conclude that length is irrelevant. "Although rates of change varied in line with the GEL, most people nonetheless responded within defined boundaries as described in the dose-response literature." They coin a phrase for that, "boundaried responsive regulation": people respond at different rates, and most of them respond within a bounded window. They also note that "findings varied depending on methodological criteria used."
What this does not show
No one was randomised to a length of treatment. A person who stays longer because they came in worse is not evidence that staying longer made them worse, or better. The studies came from routine services, so long term private therapy is barely represented.
Worth asking
If I have been in therapy a long time, what, measured, has changed?
Source
A systematic review and meta-analysis of the good-enough level (GEL) literature — Bone C, Delgadillo J, Barkham M (2021)
Reputable peer-reviewed journal
Read the source: https://doi.org/10.1037/cou0000521
DOI: 10.1037/cou0000521
How this was scored
- Study design
- Systematic review of observational studies
- Funding
- Funding not disclosed
- Published in
- Reputable peer-reviewed journal
- Sample size
- 114,123
- Preregistered
- Yes
- 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 "moderate evidence". Reasonable evidence with real limitations. It scores 65 out of 100 on our published rubric. One caveat travels with that badge: A meta-analysis of observational routine-care studies, so the null association is descriptive, not causal. The confidence interval on the main estimate is wide (-0.70 to 0.36), which is consistent with a moderate association in either direction as well as with none. The authors themselves say results depended on the methodological criteria applied. 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?
A systematic review and meta-analysis of the good-enough level (GEL) literature — Bone C, Delgadillo J, Barkham M (2021). Published in: Reputable peer-reviewed journal. DOI: 10.1037/cou0000521. 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: Systematic review of observational studies. 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.