Kerdabadi et al. (2024) — a meta-analysis of “polyvagal” interventions
The fourth and last of the human’s Polyvagal-folder sources, and the one that changes axis. The debate core — Porges (2023) vs Grossman (2023) — is about whether Polyvagal Theory’s physiological premises are true. This paper asks the separate, clinical question both sides agree is separate: do interventions carried out under the polyvagal banner help? Its answer — a small but statistically robust pooled benefit — is best read not as support for the theory but as an illustration of the theory’s dispensability, because most of what it pools is generic relaxation.
A bilingual paper (English abstract, Persian body) in an Iranian journal; read via pdftotext (born-digital). Ethics code IR.IAU.CTB.REC.1402.162; drawn from the first author’s doctoral dissertation; no funding; no declared conflict.
What it did
A PRISMA-guided systematic search (1994–2023, eight Latin databases + three Persian ones) on keywords polyvagal / vagus nerve / autonomic nervous system / vagal tone. Of 4021 records, 9 studies met the inclusion criteria (experimental/quasi-experimental with the statistics needed to compute an effect size), yielding 26 effect sizes entered into Comprehensive Meta-Analysis v3 as Hedges’s g.
The 9 studies and their labelled interventions:
| study | ”polyvagal” intervention | population / outcome |
|---|---|---|
| Kawai 2023 | Safe and Sound Protocol (SSP) | adult autism; social vulnerability (exploratory pilot) |
| Heilman 2023 | Safe and Sound Protocol (SSP) | autism; sensory / GI / selective-eating (single-arm) |
| Rizvi 2023 | ”integrated polyvagal exercises” + knee reinforcement | knee osteoarthritis, women; QoL (RCT) |
| Magnon 2021 | one session deep-slow breathing | anxiety, vagal tone |
| Hoseinpourfard 2020 | paced-breathing HRV biofeedback | sleep disorder |
| Meier 2020 | standardized massage | stress, psychophysiological relaxation |
| De & Mondal 2019 | yogic postures (asana) | autonomic / parasympathetic tone |
| Lü 2013 | positive psychotherapy | cardiac vagal tone in low positive affect |
| Barnes 2011 | mindfulness + cold-face dive reflex | approach motivation |
The result, and how big it actually is
The combined effect is Hedges’s g ≈ 0.26 (reported with a negative sign, −0.26, because many outcomes are coded as symptom reduction), 95% CI |0.18–0.34|, Z = −6.24, p < .001, significant under both fixed- and random-effects models (random-effects point estimate −0.28). The authors describe this as a “medium” effect in the English abstract and repeatedly as a “large” (بزرگ) effect in the Persian body.
Both are wrong. By Cohen’s own conventions (small 0.2, medium 0.5, large 0.8), g ≈ 0.26 is a small effect. The paper’s central recommendation — that clinicians adopt these interventions — rests on a magnitude it consistently overstates, in two different directions in the same document.
For publication bias the authors run three checks and clear all three: classic fail-safe N = 236 (studies needed to null the effect), Begg & Mazumdar rank correlation non-significant (τ ≈ 0.29, p ≈ 0.77 two-tailed), and Duval & Tweedie trim-and-fill adds no studies on either side. What they do not report is heterogeneity: the trim-and-fill table gives a random-effects Q ≈ 204 on 25 degrees of freedom, i.e. I² ≈ 88% — very high dispersion for a single pooled estimate lumping massage, yoga, breathing, biofeedback and psychotherapy across sleep, anxiety, sensory sensitivity, QoL and motivation. No moderator or subgroup analysis is offered.
Why this is dispensability evidence, not validity evidence
The wiki has recorded twice already (Bonaz, Weng) that substantial trauma- and health-relevant vagal results arise without invoking Porges — evidence about the framework’s dispensability rather than its truth. This paper is a third, sharper instance, and from the pro-PVT side.
Its “polyvagal interventions” are, with one exception, techniques that long predate Polyvagal Theory and are explicable by ordinary parasympathetic activation / raised RSA: standardized massage (Meier), yogic postures (De & Mondal), a single session of slow breathing (Magnon), HRV biofeedback (Hoseinpourfard), mindfulness and the mammalian dive reflex (Barnes), positive psychotherapy (Lü). Only the Safe and Sound Protocol (Kawai, Heilman) is a Porges-designed intervention — and it is the one with the weakest designs here (an exploratory pilot and an uncontrolled single-arm study). The meta-analysis pools “things that raise vagal tone,” finds they modestly help, and attributes the benefit post hoc to the theory.
That is exactly the move Grossman flags: PVT-inspired therapies may help while the theory’s phylogenetic and anatomical premises are false, because the therapies do not depend on those premises being true. So even taken at face value, this paper does not adjudicate is-polyvagal-theory-valid — and its construct inflation is itself an exhibit for the critic’s side. Filed as a clinical-utility datum: a small pooled benefit for a heterogeneous bundle of relaxation techniques, of no evidential weight for the theory’s contested mechanism, and weaker than its own conclusion claims.
No hard contradiction
Nothing here contradicts existing wiki content. It sits on the clinical axis the debate page already separates out, and the “generic vagal techniques help without needing PVT” reading reinforces the dispensability observation on polyvagal-theory and the “clinical utility is a separate axis” point on is-polyvagal-theory-valid. Recorded with its magnitude, heterogeneity and construct-inflation flaws named rather than smoothed over.