The values of the payment rates will rise or fall depending on the advertising contracts that team Shorte.st firm. I'll explain (example); a game company hires Shorte.st for online advertising, it needs public coming from USA, then the rate for the United States rises, because advertising is focused mainly to that country.
You can also see the payout rates "eCPM Updated Daily" here : http://shorte.st/payoutrates
Hope this helps ;)
~Mohammed.
-- Edited by Mohammed on Thursday 24th of July 2014 11:33:18 PM