# FEATURE_SLOT_SUBSTITUTION -- Transportability by Claim Type

**Owner:** Epistemic Output Layer (S4). **Library:** Private RAM. **Consumers:** S4 only.

Transportability computation uses **feature-slot substitution**, not reweighting. The dominant transportability signal differs by claim type, and for normative + interpretive the primitive itself is substituted (mechanism-stability is not the right primitive). Reweighting alone collapses the schema. R3.3 load-bearing.

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## 1. Per-Claim-Type Slot Table

| Claim type | Slot label | Primitive | Tool / rubric | Output | Type-coded caveat |
|---|---|---|---|---|---|
| Descriptive | `sampling_representativeness` | Brunswik X-validity match; PIET-T Population block only (not full 44) | PIET-T Population criteria | `{slot, score, rationale, piet_t_population_subscores}` | none unless `axis-not-computable` |
| Causal | `mechanism_context_coupling` | CMO decomposition (C -> C' delta + M stability); Pearl-Bareinboim selection-diagram check where structure is articulable; PIET-T full 44 as feature vector | Pawson-Tilley CMO; Shadish-Cook-Campbell X/T/Y/C; Pearl-Bareinboim transport calculus; PIET-T | `{slot, score, rationale, c_delta, mechanism_stability, piet_t_full_subscores, pearl_transport_check: decidable\|undecidable\|out-of-scope}` | none unless `axis-not-computable` |
| Predictive | `covariate_shift + mechanism_stability` | Pearl-Bareinboim transport formula directly; covariate-shift between training and decision context + mechanism-stability sub-score | Pearl-Bareinboim; Shadish-Cook-Campbell | `{slot, score, rationale, covariate_delta, mechanism_stability, pearl_transport_check}` | none unless `axis-not-computable` |
| Normative | `value_commensurability` | Substitute slot. Compute value-commensurability between study-context and decision-context value frames. Mechanism-stability is NOT computed. | Metaethical argument; policy-logic; Dorst frame innovation | `{slot, score, rationale, type_coded_caveat: "value-commensurability-required"}` | **MANDATORY:** `value-commensurability-required` |
| Interpretive | `reader_relevance_proxy` | Substitute slot. CERQual: methodological limitations + coherence + adequacy of data + relevance. Researcher-side transport is NOT claimed. | GRADE-CERQual; Lincoln-Guba thick description; Drisko contradiction | `{slot, score, rationale, cerqual_subscores, type_coded_caveat: "reader-judgment-required"}` | **MANDATORY:** `reader-judgment-required` |

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## 2. Why Substitution (Not Reweighting)

Reweighting assumes the underlying primitive is the same and only the weights differ. For normative and interpretive claims the primitive is wrong:
- **Normative:** mechanism-stability answers "does the mechanism still fire under context shift?" The question is irrelevant; a normative claim transports via value-commensurability ("do the context's value frames accept the ought-statement?"). Reweighting mechanism-stability to zero is NOT the same as computing value-commensurability.
- **Interpretive:** Lincoln-Guba 1985 and Drisko 2025 (CONTRADICTION SOURCE) argue researcher-side transportability is not in principle computable for interpretive claims. Transferability is the reader's judgment given thick description. CERQual gives us a reader-relevance proxy -- a defensible, caveated approximation -- NOT a transported score.

Reweighting masks the category mismatch. Substitution surfaces it. E6 catches any reweighting masquerade at render validation.

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## 3. PIET-T Binding (descriptive / causal / predictive)

PIET-T (Schloemer & Schroder-Back 2018, *Implementation Science*) provides 44 practitioner-validated criteria across Population / Intervention / Environment / Transfer. Map:
- **Descriptive:** Population block only (sampling representativeness). Using full 44 is overkill and dilutes the signal.
- **Causal:** full 44. PIET-T's Population/Intervention/Environment/Transfer map to Shadish-Cook-Campbell X/T/C/Y and supply the concrete feature vector for the C -> C' delta.
- **Predictive:** full 44 plus covariate-shift computation, fed into Pearl-Bareinboim transport formula.

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## 4. CERQual Binding (interpretive)

CERQual (Lewin et al. 2018) has four components used as the `reader_relevance_proxy` sub-scores:
- **Methodological limitations:** quality of primary studies contributing to the interpretive finding.
- **Coherence:** fit between data and interpretation.
- **Adequacy:** richness and quantity of data supporting the finding.
- **Relevance:** applicability of finding-context features to the decision-context (this is the reader-side transferability surrogate).

Render these as sub-scores under the `reader_relevance_proxy` slot output. NEVER collapse into a single CERQual grade for a transportability render (CERQual itself does have an overall confidence rating, but exporting ONLY that grade collapses transportability back to a single score and breaks the three-axis doctrine).

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## 5. `axis-not-computable` (all claim types)

If the feature slot cannot be filled (decision context missing; study context ungrounded; claim type mis-typed upstream): emit `{axis_not_computable: true, reason: <string>}`. Do NOT impute. Do NOT fall back to "moderate." Do NOT silently omit the axis -- the validator at Phase E requires an axis object or an `axis-not-computable` object for every claim.

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## 6. Comparability Rule

Scores are ONLY comparable across claims when BOTH the claim type AND the slot label match. Different slot labels are not arithmetically compatible. Render side-by-side for cross-claim reading; NEVER compute an average, a rank, or a summary across claims with different slots.
