How often is CTR re-evaluated for bidding purposes?

Rank = CTR X bid - but how often does CTR get updated?

[limitup]

Title and meta pretty much says it all ...

As I understand it, your rank is a function of your CTR multiplied by your max bid. But exactly which CTR is used in this calculation? Is it the CTR for a particular term since the day you added it to your account, the CTR for that term over the past month, the past week, CTR from yesterday or?

[NedProf]

Limitup:
For as far I know the algorithm of AdWords is more complicated then you suggest. There's also a historical factor and a kind of correction factor for the position of the ad.

I think the CTR is the CTR over the last 1000 impressions and is continue calculated.

[Tropical Island]

I would also assume that it is an on-going process which would explain the changing posistion of some ads during the course of the day.

[limitup]

Can anyone confirm that it's the CTR over the last 1,000 impressions?

[AdWordsAdvisor]

Can anyone confirm that it's the CTR over the last 1,000 impressions?

limitup, it is actually the all-time CTR for the keyword that matters, with the most recent 1000 impressions being weighted a bit more heavily.

One way to look at it: every single time a keyword has an impression, it's CTR has changed. The same is true if it has both an impression and a click. The AdWords system works on this basis, and weights to most recent 1000 impression more heavily. However, if you have a truly horrible 'most recent 1000', your past history, assuming it is at least reasonably strong, will save you.

AWA

[suzyvirtual]

I just want to double check that this is for the keyword and not the ad. I recently experienced a massive drop in positions after changing some ads, while leaving the CPC the same.

[NedProf]

The ads are related to the keywords. So bad ads -> bad CTR on the individual keywords -> lower rank on the individual keywords.

[dmerton]

I have told, via Google support that CTR for the purpose of position is evaluted on the spot, every time, because it is constantly changing. Also, it is important to also know that it is your lifetime CTR, even if you delete and then add the term again, G remembers your CTR. Hope this helps.