I recently purchased a web site that was ranked number 1 on Google. Within 24 hours of the ownership change, Google dropped the ranking significantly to page 5. Does Google look at DNS changes, and could this be the reason for the lower ranking? Any other ideas of what could have caused this? FYI, the ranking in Yahoo was unaffected.

My initial reaction to this question was that you were trying to draw a casual relationship from correlational data (yeah, my Masters degree comes out in weird ways sometimes :-) ) and that this was basically a case of Google doing a "dance" coincidentally with your ownership change.

I thought it would be useful to ask some real SEO experts, however, so I sent out your query to a search engine marketing list I'm involved with, and the resultant answers were, well, darn surprising!

More than one person reported that they'd changed DNS records and almost instantly lost all ranking on Google (that is, their resultant placement for a given search term dropped precipitously). One data point here is that a while back Google actually signed up as a domain registrar, so they certainly have access to all the backend data that they could use. Additionally, one of Google's search patents states:

"The method of claim 1, wherein the one or more types of history data includes domain-related information corresponding to domains associated with documents; and wherein the generating a score includes: analyzing domain-related information corresponding to a
domain associated with the document over time, and scoring the document based, at least in part, on a result of the analyzing."

Interesting, eh?

One chap reports that he received confirmation from Google's engineers that the "trust" for a domain is reset if any domain registration info changes. A change in IP, however, doesn't affect the "trust" points, but does cause the search engine to reevaluate link counts, etc.

Nonetheless, there are some important questions left unanswered, however, that include whether you changed the IP address of the domain and whether you're seeing a drop in traffic, rather than just a drop in SERP?

Ah well, it indeed looks likely that your theory is correct in any case, that your Search Engine Results Placement (SERP) dropped because you changed domain records by purchasing the domain. Hopefully this will be temporary.