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From Swing Voters via ilovecharts
This is a great example for students of how longitudinal measurement is sometimes used in polling to understand the effect of a specific event. The post-speech numbers alone tell us a bit about Obama’s popularity, but nothing about the speech. With a pre/post on the speech, we can use the post-speech gain to understand the speech’s effect.

From Swing Voters via ilovecharts

This is a great example for students of how longitudinal measurement is sometimes used in polling to understand the effect of a specific event. The post-speech numbers alone tell us a bit about Obama’s popularity, but nothing about the speech. With a pre/post on the speech, we can use the post-speech gain to understand the speech’s effect.