For example, if the reason you were considering not voting was bad weather on election day, and you managed to discard that reason as one you won't be moved by in a voting decision, this decision would be common to many people irrespective of their candidate. By deciding to vote anyway, you establish that people in similar situations do vote.

Could you please tell me what "to establish" means in the last sentence?

(Your comment made me spit out my tea. I know almost nothing about U/TDT.)