Also, Google always tells us that the highest paying ad is the one that's showing first on your page. But what if for whatever reason, the user clicks on the LAST ad (which is presumably among the lowest paying) on your page? If you use more than one ad unit, that's always a possibility.
Clicks is clicks is clicks. I get .01 clicks and I get 9.00 clicks. Obviously I prefer the latter, but the former add up too. I'll take them all.
Updated? Nobody knows. I doubt it. But in the case of clicks deemed invalid for whatever reason, they used to remove the earnings but leave the (empty) clicks and impressions. Now if they detect invalid activity, they're removing earnings, clicks and impressions.
@netmeg, I thought it was top performing ads first, whether they pay more per click or not, the ones that make more money over time. Recent example; new advertiser shows up with a hot ad and highly targeted to the site, CTR doubled, CPC dropped 45%. Was that site a winner? Didn't feel like it when you figure that that site barely made a few dollars extra that day but the retention rate dropped because the "hot" ad took them offsite.
Well yea, technically it is. But if you're talking text ads and you have more than one ad unit per page, by the time someone clicks on one of the lowerr ads, because it still is an auction of sort, odds are those lower ads don't pay much.
I would love to see some stats on how often the top ad in each ad unit gets clicked (vs other ads) but of course Google will never tell us that.