Any ideas what causes this kind of drop in rank?

[dickbaker]

Throughout all of the updates and other upheavals with Google over the last six years, the pages on my site have weathered the storms fairly well.

This time, though, there's a couple of changes that have me scratching my head.

There are a couple of key phrases that have been page one for years that have now changed. One is "Acme widgets." This phrase was #4 to #8 throughout 2008, and #5 or #6 in 2009. Back in February in moved to #14, and it's now at #28.

A variation of the phrase, "Acme thingamajigs," is still page one.

Another page on the site is fairing similarly.

Does anyone have any ideas as to what might be happening here? I looked at backlinks for the page, but didn't see anything unusual.

[tedster]

This sounds mysterious, Dick - some change that is coming at you from "200 factors" land. It could even be an algorithm change and your site is a "canary in the coal mine".

The fact that the change didn't affect one synonym but did affect the other seems to point to phrase-based indexing [webmasterworld.com]. That is an area where there seems to be more activity recently -- including a newly granted patent [patft.uspto.gov]. I'm still studying that particular patent and don't have anything definitive to say right now, except that I suspect Caffeine may be using some of that approach.