Figure 1From “What is external validity? A result needs a transfer boundary”
The external-validity transfer matrix
A result can be internally credible and still need a new argument before it is transported to a different target.
Figure 1The external-validity transfer matrix
Source: Author's synthetic transfer matrix grounded in Egami and Hartman (2023) and Campbell (1979). All rows, effects, and decisions are illustrative.

Source and evidence
Each line names a claim related to this exhibit, its source, and how it was checked.
- A EH23-C1 "we propose a formal framework that encompasses four dimensions of external validity x t y and c validity populations treatments outcomes and contexts"Egami & Hartman. (2023)
- A EH23-C2 Two goals, not one: "effect generalization generalizing the magnitude of causal effects" and "sign generalization generalizing the direction of causal effects", each with its own estimators and assumptionsEgami & Hartman. (2023)
- A EH23-C3 "effect generalization generalizing the magnitude of causal effects", for which the authors "introduce three estimators of the target population causal effects"Egami & Hartman. (2023)
- A EH23-C4 "sign generalization generalizing the direction of causal effects", for which they "propose a novel multiple testing procedure under weaker assumptions": a different target needs a different toolEgami & Hartman. (2023)
- B R01-OWN-C1 External validity is target-relative; a result does not possess universal transfer by itselfAuthor framework
- B R01-OWN-C3 Changing one transfer field changes the target claim boundary before a verdict is offeredAuthor boundary
- B R01-OWN-C4 A self-serve small-business experiment does not automatically answer an enterprise implementation targetAuthor synthetic illustration
- B R01-OWN-C7 Replication, transport, and analogy are different decisions with different evidentiary burdensAuthor framework
Grades: A, verified against the printed page of the primary source · B, primary source, text layer only · C, authoritative secondary · D, reported.
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What is external validity? A result needs a transfer boundary
External validity asks whether a result transfers across a named population, treatment, outcome, and context. Name the target before generalizing.
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Table 3Table
What does a transfer matrix look like?
What is external validity? A result needs a transfer boundary

Table 1Table
Which four dimensions change the transfer question?
What is external validity? A result needs a transfer boundary

Table 4Table
How should a team review a transfer claim?
What is external validity? A result needs a transfer boundary
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