How come impressions are not really accurate?

[bostonseo]

I have never believed the impressions reported by AdWords to be 100% accurate. My account manager has always insisted that they are so I told them that I would do a test and see :)

So I picked 1 campaign that has about 10 keywords (all exact match and all active). I went yesterday to Google.com and searched on each of the 10 keywords and saw my ads - I did not click on any of them. Today I went in and looked to see if at least every term reported 1 impression - and just what I thought,,,,7 of the 10 terms DID NOT report an impression from yesterday.

I have them looking into why this is. Has anyone else had them look into this?

[trinorthlighting]

It probally only records impressions per ip address. So if you looked at 100 ads from your ip address it only registered as one.

[bostonseo]

Ahhh I don't think that's it; that would throw off CTR rate.

[AdWordsAdvisor]

I have never believed the impressions reported by AdWords to be 100% accurate.

From the AdWords FAQ (with bolding added for emphasis) by way of one possible explanation:

...proprietary technology analyzes clicks and impressions in an attempt to determine whether they fit a pattern of use intended to artificially drive up an advertiser's clicks or impressions, or a publisher's earnings.

Ahhh I don't think that's it; that would throw off CTR rate.

One might think of analyzing impressions as protecting the accuracy of the CTR, rather than throwing it off.

AWA

[bostonseo]

I got a response that basically said nothing - you have to read between the lines to see that the real answer is 'we don't comment on how our systems work'.