Reliable Change Index: Is Treatment Progress Real?

Client Symptom Scores

Pre-treatment score 32

Post-treatment score 14

Measurement Properties

Test–retest reliability r_xx 0.85

Population SD (σ) 9.0

Outcome

—Adjust the sliders above.

Reliable Change Index

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SE of difference

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Clinically-significant cutoff (c)

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Dysfunctional (clinical) population, N≈250 Functional (normative) population, N≈250 Pre-treatment score Post-treatment score

How it works

Jacobson & Truax (1991) proposed two questions every psychotherapy outcome must answer: did the client change more than measurement error alone could explain, and did they end up statistically closer to a healthy population than a clinical one?

Standard error of measurement:  SEM = σ·√(1 − r_xx)
Standard error of difference:  SE_diff = SEM·√2
Reliable Change Index:         RCI = (post − pre) / SE_diff

|RCI| ≥ 1.96  →  reliably changed (p < .05, not just noise)
|RCI| <  1.96  →  change indistinguishable from measurement error

Clinically significant cutoff (functional/dysfunctional crossover):
c = (σ_clin·μ_norm + σ_norm·μ_clin) / (σ_clin + σ_norm)

Pre / Post sliders — the client's symptom score before and after treatment on a 0–63 scale (styled after common inventories such as the BDI-II); lower is healthier.
r_xx — the measure's test–retest reliability. A noisier instrument (lower r_xx) inflates measurement error and makes the same raw change less reliable.
σ — the standard deviation of scores in the general population, the other input to measurement error.
The red and green point clouds are 250 samples each drawn from fixed reference distributions (clinical: μ=30, σ=10; normative: μ=8, σ=6) — they show where a "sick" and a "well" population actually sit on this scale, so a raw score can be read against real context instead of a bare number.
Real-world relevance: this is the standard statistic clinical trials and single-case practitioners use to separate genuine treatment response from random fluctuation in self-report measures — required reporting in most psychotherapy efficacy research.

Pre Post Cutoff c

Symptom severity score (0 → 63) — lower is healthier →

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