SSI = Σ(severity × salience) / n. Severity scales: withheld (1.0), delayed (0.5), revised (0.3). Salience scales: census (1.0), Consumption Expenditure Survey (0.8), PLFS (0.7), other (0.6). The index is event-based, so a single year's score is the weighted average of that year's statistical incidents.
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This is one of 36 standing analyses drawn from the Some Perspective dataset. It is not dated commentary: it describes a relationship in the data that holds across the series, and it is regenerated whenever the underlying dataset is refreshed. The figures quoted here reflect the 2026-08-15 data vintage.