Weekly therapy got people better faster than fortnightly, but not further
In 21,488 university counselling clients over 17 years, weekly attendance produced steeper recovery curves and faster clinically significant gains than fortnightly. Few differences were found in the total amount of change.
Reasonable evidence with real limitations. how we score evidence
Caveat on this rating: A single university counselling centre with a young, mostly White sample; frequency was chosen, not assigned. The effect on speed is between small and medium by the authors' own description, and the paper reports no difference in total change, so it argues for efficiency rather than for a better end result.
Most dose research counts sessions. This study asked about the gap between them.
Significant findings
Erekson, Lambert and Eggett used seventeen years of session by session outcome data (the OQ-45) from 21,488 clients at a university counselling centre. They modelled each person's change over time with session frequency built in, then compared the people who came roughly weekly with the people who came roughly fortnightly.
"More frequent therapy was associated with steeper recovery curves (Cohen's f2 = 0.07; an effect size between small and medium)." Comparing the two groups directly, "clinically significant gains were achieved faster for those attending weekly sessions."
Then the qualifier: "however, few significant differences were found between groups in total amount of change in therapy." Weekly clients got to the same place sooner. They did not, on average, get further.
The authors' conclusion: "Session frequency appears to be an impactful component in delivering more efficient psychotherapy."
The other direction
Efficiency is not everything. A person who can only manage fortnightly sessions is not, on this evidence, getting a worse result at the end, only a slower one. And the clients here were young adults (mean age 22.5) at one American university centre, which is not every setting.
What this does not show
Frequency was not assigned. People who attended weekly may have been more motivated, more available, or more distressed. The effect size is between small and medium, and the study says so in the abstract.
Worth asking
If sessions are limited, is it better to take them closer together?
Source
The relationship between session frequency and psychotherapy outcome in a naturalistic setting — Erekson DM, Lambert MJ, Eggett DL (2015)
Reputable peer-reviewed journal
Read the source: https://doi.org/10.1037/a0039774
DOI: 10.1037/a0039774
How this was scored
- Study design
- Cohort study
- Funding
- Funding not disclosed
- Published in
- Reputable peer-reviewed journal
- Sample size
- 21,488
- 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 "moderate evidence". Reasonable evidence with real limitations. It scores 55 out of 100 on our published rubric. One caveat travels with that badge: A single university counselling centre with a young, mostly White sample; frequency was chosen, not assigned. The effect on speed is between small and medium by the authors' own description, and the paper reports no difference in total change, so it argues for efficiency rather than for a better end result. 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?
The relationship between session frequency and psychotherapy outcome in a naturalistic setting — Erekson DM, Lambert MJ, Eggett DL (2015). Published in: Reputable peer-reviewed journal. DOI: 10.1037/a0039774. 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.