Policy influence is measured by whether the change was adopted within four years.

Evidence

Our dependent variable is a measure of whether or not the policy change proposed in each survey question was actually adopted within four years after the question was asked. (It turns out that most of the action occurred within two years). — Martin Gilens and Benjamin I. Page, Testing Theories of American Politics, 64

Categorization

• QUESTION: Four-year adoption window as the outcome - worth comparing against how citizen-initiated vs elite-initiated changes differ in speed.