Why is CTR higher first half of day but more impressions last half?

[trader]

Ever since we have been with Adsense (a long 2-1/2 yrs) it's noticable the first half of the day almost always seems to enjoy a higher CTR than the last half of the day.

As a typical day progresses our CTR is usually on an ongoing and steady decline from about mid-day thru midnight, but the number of impressions is better the last half of the day vs before noon.

This may be due to some kind of an odd correlation between more impressions equaling a lower CTR. However, not sure about that relationship which makes little sense why that would be so, IMO.

This observation is based on a large number of diverse category and subject websites running Adsense.

Anyone else observed this pattern or know why it happens?

[http200]

me too, but i don't know the reason.

[ning]

Advertisers daily budgets runs out = less competition = less targetted ads = lower CTR = less income.

[FrostyMug]

i notice this too all the time. probably for the reasons already given above.