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The MORT programme incorporated know-how that had the best standard of evidence available, and would use logic and expert judgement to fill gaps in knowledge.

Johnson’s “Hierarchy of Proof”

“By and large the system is an assemblage of individual ideas with varying degrees of proof. Many concepts are proposed safety applications of general theory developed by related sciences, e.g., behavior or organization.

An ordering of the degrees of support for a specific idea or component could be:

1. Scientific evidence:

a. Safety application, e.g., human factors engineering.

b. General theory (not specifically safety), e,g., acceptance of innovations.

c. General safety theory generated from findings, e.g., Haddon's energy barrier notion.

2. Intermediate proofs:

These could include widespread, strong convictions of values, e.g., Job Safety Analysis in steel and other industries; literature search as a standard practice in science; or codes, standards, and regulations in safety law and practice.

3. Minimal proofs:

This would include some, a few, or a single closely related usage with some proof of value, e.g., trend analysis without controls or managerial opinion based on stated criteria, and includes some traditional approaches largely untested.

4. Logic or common sense (to fill gaps).

5. Innovative hunch (to fill gaps).

In MORT the emphasis has been to utilize ideas as far up in the hierarchy as possible, but at the same time, fulfil the logical requirements where necessary”.   

(Johnson, 1973; p11)