Sudden Drops to Specific Google Search Impressions in WMT

[doshu]

Today I was going back over the month of October and noticed two queries(so far) in Google Webmaster Tools completely drop off in impressions even though our average position is in the 1-2 range and remains unchanged.

I understand if our ranking dropped that obviously would cause the impressions and clicks to drop, but that is not the case.

What if anything can Google do to change the way an entire search query is displayed? The same thing happened to another similar query on the same day.

I can't imagine people just picked that day to modify how they search.

Any help in shedding light on what I am missing or what could be going on would be greatly appreciated.

Here is a image of the Webmaster Tools graph: [tinypic.com...]

[aakk9999]

Are you still average position in 1-2 range if you reduce the period of report to the time where your impressions have dropped?

For instance, if you reduce reporting to be period from 17 - 29th October and compare that average position with period from 24 September to 16 October, are the average positions the same or very similar for both periods?

What I am getting to is that the data from 24 Sept - 16 Oct can skew your average position reporting.

[doshu]

When I reduce the reporting to Oct. 17th through the 29th the average remains at 1.7.

So before the drop it was 1.7 and after the drop it was 1.7, but impressions have dropped nearly 70%.

[aakk9999]

Hmm.. this can still be possible without number of searches being dropped.

Lets assume that for the keyword where you had drop in impressions, there are two data centres that return results and that in the data centre #1 you appear at position 1-2 and in data centre #2 you do not appear at all.

If Google starts to serve more results from data centre #2, then your number of impressions will drop, but the average position (now calculated based solely on data centre #1) would still be 1-2 whilst the number of searches may have remained constant.

This impression drop would also happen if you had significant drop in SERPs shown by data centre #2 which results in your site being so far (on page 50 for example) that nobody pages to it and hence you got no impression for this term.