Crises can reorder trust, priorities, and party reputations across many age groups.

Use comparable measures before and after the event. Parallel movement across several cohorts supports a period effect; lasting distinctiveness confined to a cohort suggests a formative imprint, while different exposure can explain unequal movement around the shared change.

A period effect appears when an event moves several cohorts in the same historical interval, although the size or duration of change may differ by age and experience. Evidence should include attitudes before the event and comparable measures afterward. Without that baseline, a difference observed after a crisis may be an older cohort difference rather than event-driven change. Events are also interpreted through parties, media, leaders, and personal experience. The same recession may reduce trust broadly while affecting homeowners, recent graduates, and retirees differently. Shared timing supports a period effect; unequal impact explains variation around it. If every age group changes immediately but only the youngest cohort retains the change, the event may produce both period and cohort effects.

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