Importance:
AWA
AWA explains that the most recent 1000 ad impressions are weighted heavier in determining keyword status, but positioning in determined "in the moment".
AdWordsAdvisor Says: [
Link to quote]
Hi all - just getting here, rather late, after a very busy morning!
"I'm 99% certain keyword status is determine by last 1000 impressions.
Maybe the ctr in position formula is all time and I've confused them over time.
AWA, could you please clarify this for us? "
In terms of positioning, it is the CTR of the keyword in the moment it is searched on that matters - but this is a reflection of its entire history.
The most recent 1000 impressions are weighted (slightly) more heavily, though the entire past history is considered as well. Part of the reason for considering the entire past history it to protect a keyword that has worked well for a long time from being disabled if it has a truly miserable 'most recent' 1000 impressions.
I hope I am answering the right question here - this thread has covered a lot of ground!
AWA