Scientific Evidence

What actually makes therapy work.

Decades of clinical research point to a single variable as the strongest and most replicated predictor of therapeutic success — and it is the variable our solution is built around.

The findingsMeta-analysis by Kazantzis et al., 2016
Quantity of homework completed
g ≈ 0.79
Large effect on outcomes at end of treatment.
When patients actually complete the homework assigned between sessions, the clinical improvement measured at the end of therapy is large in magnitude (Hedges' g).
15 studies · n = 1,537 · 95% CI [0.57, 1.02]
Quality of homework — follow-up
g ≈ 1.07
Even larger effect at follow-up. Changes last.
It is not enough to do the homework: doing it with quality predicts even greater improvements weeks and months after therapy ends. People do not relapse.
Behavior Therapy · 47(5), 755–772

What it means, in plain terms.

In psychotherapy, clinical effects are rarely enormous. An effect considered “large” (Hedges' g ≥ 0.80) is exceptional — equivalent to a change that the patient, their family and the clinician can clearly recognize in daily life.

Kazantzis et al.'s 2016 meta-analysis, published in Behavior Therapy, found exactly that: when patients complete the homework their therapist assigns between sessions, the effect on clinical outcomes is large. And when that homework is done with quality, the benefit at follow-up is even greater than at the end of treatment.

“The quality of practice outside the consulting room predicts greater improvements at follow-up than those observed at the end of therapy.”

It is an unusual finding in the clinical literature: most interventions lose effect over time. Here, the changes grow. That is why we built our entire solution around this single variable: getting the homework done, and getting it done well.

The Literature

Peer-reviewed studies that support our approach.

Primary study
  1. Kazantzis, N., Whittington, C., Zelencich, L., Kyrios, M., Norton, P. J., & Hofmann, S. G. (2016). Quantity and quality of homework compliance: A meta-analysis of relations with outcome in cognitive behavior therapy. Behavior Therapy, 47(5), 755–772. doi.org/10.1016/j.beth.2016.05.002
Supporting meta-analyses
  1. Kazantzis, N., Deane, F. P., & Ronan, K. R. (2000). Homework assignments in cognitive and behavioral therapy: A meta-analysis. Clinical Psychology: Science and Practice, 7(2), 189–202. doi.org/10.1093/clipsy.7.2.189
  2. Kazantzis, N., Whittington, C. J., & Dattilio, F. M. (2010). Meta-analysis of homework effects in cognitive and behavioral therapy: A replication and extension. Clinical Psychology: Science and Practice, 17(2), 144–156. doi.org/10.1111/j.1468-2850.2010.01204.x
  3. Mausbach, B. T., Moore, R., Roesch, S., Cardenas, V., & Patterson, T. L. (2010). The relationship between homework compliance and therapy outcomes: An updated meta-analysis. Cognitive Therapy and Research, 34(5), 429–438. doi.org/10.1007/s10608-010-9297-z
Modern reviews and mechanism
  1. Ryum, T., & Kazantzis, N. (2024). Homework as a driver of change in psychotherapy. Journal of Clinical Psychology, 80(5). doi.org/10.1002/jclp.23627
  2. Lim, J. A., & Kazantzis, N. (2023). Integrating between-session homework in psychotherapy: A systematic review of immediate in-session and intermediate outcomes. Psychotherapy, 60(2), 232–247. doi.org/10.1037/pst0000488
  3. Kazantzis, N., Luong, H. K., Usatoff, A. S., Impala, T., Yew, R. Y., & Hofmann, S. G. (2018). The processes of cognitive behavioral therapy: A review of meta-analyses. Cognitive Therapy and Research, 42(4), 349–357.
  4. Wheaton, M. G., & Chen, S. R. (2021). Homework completion in treating obsessive–compulsive disorder with exposure and ritual prevention: A review of the empirical literature. Cognitive Therapy and Research, 45(2), 236–249. doi.org/10.1007/s10608-020-10125-0
Key empirical studies
  1. Burns, D. D., & Spangler, D. L. (2000). Does psychotherapy homework lead to improvements in depression in cognitive-behavioral therapy or does improvement lead to increased homework compliance? Journal of Consulting and Clinical Psychology, 68(1), 46–56.
  2. Conklin, L. R., & Strunk, D. R. (2015). A session-to-session examination of homework engagement in cognitive therapy for depression: Do patients experience immediate benefits? Behaviour Research and Therapy, 72, 56–62.
  3. Decker, S. E., Kiluk, B. D., Frankforter, T., Babuscio, T., Nich, C., & Carroll, K. M. (2016). Just showing up is not enough: Homework adherence and outcome in cognitive-behavioral therapy for cocaine dependence. Journal of Consulting and Clinical Psychology, 84(10), 907–912.
  4. Stirman, S. W., Gutner, C. A., Suvak, M. K., Adler, A., Calloway, A., & Resick, P. A. (2018). Homework completion, patient characteristics, and symptom change in cognitive processing therapy for PTSD. Behavior Therapy, 49(5), 741–755.
A note on honesty

We do not promise absolute certainties. We promise to work on the variable that science has identified as the most important.

No psychological treatment works for 100% of people. What we can say, with replicated backing across four separate meta-analyses, is that adherence to and quality of between-session homework is one of the strongest and most consistent predictors of therapeutic change — comparable in magnitude to the effect of the therapeutic alliance itself.

That is why we built our tool around that variable. We are not reinventing psychotherapy; we are strengthening it at the point where the evidence says it most often breaks down.