Explaining algorithm updates and data refreshes

A thread on WMW started Dec. 20th asking whether there was an update, so I'm taking a break from wrapping presents for an ultra-quick answer: no, there wasn't.

To answer in more detail, let's review the definitions. You may want to review this post or re-watch this video (session #8 from my videos). I'll try to summarize the gist in very few words though:

Algorithm update: Typically yields changes in the search results on the larger end of the spectrum. Algorithms can change at any time, but noticeable changes tend to be less frequent.

Data refresh: When data is refreshed within an existing algorithm. Changes are typically toward the less-impactful end of the spectrum, and are often so small that people don't even notice. One of the smallest types of data refreshes is an:

Index update: When new indexing data is pushed out to data centers. From the summer of 2000 to the summer of 2003, index updates tended to happen about once a month. The resulting changes were called the Google Dance. The Google Dance occurred over the course of 6-8 days because each data center in turn had to be taken out of rotation and loaded with an entirely new web index, and that took time. In the summer of 2003 (the Google Dance called "Update Fritz"), Google switched to an index that was incrementally updated every day (or faster). Instead of a monolithic monthly event, the Google would refresh some of its index pretty much every day, which generated much smaller day-to-day changes that some people called everflux.

Over the years, Google's indexing has been streamlined, to the point where most regular people don't even notice the index updating. As a result, the terms "everflux," "Google Dance," and "index update" are hardly ever used anymore (or they're used incorrectly  ). Instead, most SEOs talk about algorithm updates or data updates/refreshes. Most data refreshes are index updates, although occasionally a data refresh will happen outside of the day-to-day index updates. For example, updated backlinks and PageRanks are made visible every 3-4 months.

Okay, here's a pop quiz to see if you've been paying attention:

Q: True or false: an index update is a type of data refresh.
A: Of course an index update is a type of data refresh! Pay attention, I just said that 2-3 paragraphs ago.  Don't get hung up on "update" vs. "refresh" since they're basically the same thing. There's algorithms, and the data that the algorithms work on. A large part of changing data is our index being updated.

I know for a fact that there haven't been any major algorithm updates to our scoring in the last few days, and I believe the only data refreshes have been normal (index updates). So what are the people on WMW talking about? Here's my best MEGO guess. Go re-watch this video. Listen to the part about "data refreshes on June 27th, July 27th, and August 17th 2006." Somewhere on the web (can't remember where, and it's Christmas weekend and after midnight, so I'm not super-motivated to hunt down where I said it) in the last few months, I said to expect those (roughly monthly) updates to become more of a daily thing. That data refresh became more frequent (roughly daily instead of every 3-4 weeks or so) well over a month ago. My best guess is that any changes people are seeing are because that particular data is being refreshed more frequently.