In 1936, Saul Rosenzweig proposed something that still unsettles therapists: maybe all psychotherapies work about equally well. He borrowed the Dodo Bird's declaration from Alice in Wonderland—"Everybody has won, and all must have prizes."

Decades of research have kept this debate alive. Meta-analyses repeatedly show that different therapeutic approaches produce remarkably similar outcomes. Yet specific treatments clearly outperform others for particular conditions. Both findings are true, and both matter.

The tension between common factors and specific techniques isn't just academic. It shapes how we train clinicians, match clients to treatments, and allocate healthcare resources. Understanding what the equivalence hypothesis actually claims—and where it breaks down—offers practical guidance for clinical decision-making.

The case for therapeutic equivalence rests on robust findings. Bruce Wampold's meta-analyses consistently show that the therapeutic alliance accounts for roughly 5-8% of outcome variance—modest but reliable. Meanwhile, differences between bona fide treatments typically explain less than 1% of variance.

This isn't nothing. When you aggregate across thousands of clients, small effects matter. But the pattern holds across conditions: whether treating depression, anxiety, or relationship problems, the type of therapy matters less than whether it's delivered competently within a genuine therapeutic relationship.

Common factors extend beyond the alliance. Client expectancy—believing treatment will help—contributes independently to outcomes. So does therapist allegiance, the coherence of the treatment rationale, and opportunities for emotional experiencing. These ingredients appear in virtually every successful therapy.

Critics argue this overstates the case. Common factor estimates depend heavily on how you categorize treatments and measure outcomes. Some researchers suggest the alliance-outcome correlation reflects reverse causation: clients who improve naturally develop warmer feelings toward their therapists.

Takeaway

The therapeutic relationship and client expectations reliably predict outcomes across treatment types—what therapists share may matter more than how they differ.

The equivalence hypothesis has clear boundary conditions. For obsessive-compulsive disorder, exposure and response prevention outperforms other approaches by substantial margins. Panic disorder responds better to interoceptive exposure than to supportive counseling. Specific phobias require exposure; insight won't extinguish fear.

Trauma-focused therapies—particularly prolonged exposure and cognitive processing therapy—show advantages over present-centered approaches for PTSD. The mechanisms matter: habituation to trauma memories requires deliberate confrontation, not just supportive presence.

For personality disorders, the picture gets complicated. Dialectical behavior therapy reduces self-harm in borderline presentations more effectively than treatment-as-usual. But other structured approaches like mentalization-based therapy show comparable outcomes. Specificity may matter more at the level of structure and focus than technique.

Depression represents the most contested territory. Cognitive therapy, behavioral activation, interpersonal therapy, and short-term psychodynamic therapy all produce similar outcomes in most head-to-head comparisons. Yet behavioral activation may work faster, and cognitive approaches show advantages in preventing relapse.

Takeaway

When problems have clear behavioral components requiring specific learning—facing fears, processing trauma, building skills—technique matters more than the equivalence hypothesis suggests.

Matching clients to treatments requires navigating both findings. Start with diagnostic presentation: does this condition have treatments with demonstrated specific effects? OCD, specific phobias, and PTSD warrant evidence-based approaches as first-line options.

For conditions where equivalence holds—depression, generalized anxiety, relationship distress—client factors take precedence. Someone who values understanding their past may engage better with psychodynamic exploration. Someone seeking concrete skills may thrive with behavioral activation.

Therapist factors matter too. A skilled clinician delivering their preferred approach likely outperforms one rigidly applying an unfamiliar protocol. Competent delivery of any bona fide treatment beats incompetent delivery of the "best" treatment.

Consider treatment failures differently. When common factor treatments fail, asking about specific techniques makes sense—perhaps this client needs exposure, skills training, or a more structured approach. When specific treatments fail, common factor issues deserve attention: Is the alliance rupture? Is hopelessness undermining engagement?

Takeaway

Match specific treatments to conditions that require them; for everything else, prioritize therapeutic relationship, client preferences, and therapist competence over theoretical allegiance.

The Dodo Bird verdict isn't wrong—it's incomplete. For many presentations, common factors dominate outcomes. For others, specific techniques prove essential. Clinical wisdom means knowing which situation you're facing.

This reframes training priorities. Therapists need strong relational skills and technical competence in specific interventions. Neither alone suffices. The best clinicians calibrate their approach to what each client needs.

Rather than defending theoretical territories, we can ask better questions: What does this particular client need? What evidence guides this specific presentation? How do I deliver effective treatment while maintaining genuine connection?