Not so long ago, Google managed to impact the stats-hungry blogosphere by including subscriber numbers in its interactions with FeedBurner. Essentially, like many feed aggregators, when they pull feeds from FeedBurner, they include the counts in the transaction so that FeedBurner can then include them in their feed stats which are delivered to individual bloggers. It seems, however, that these numbers are a little shaky.
I noticed over the last couple of days a significant drop in my Google Reader numbers. This drop couldn't be attributed to losing subscribers (unless it was similar in the way to which Pharaoh lost subscribers during the Exodus) so has to be accounted for as a technical issue either on Google's end or FeedBurner.
The FeedBurner forums have a couple of threads on this topic. DevilsRejection asked about this when s/he noticed a drop of over 10% in subscribers. FeedBurner (Joe Kottke) responded:
Goggle Feed Fetcher does indeed stop sending subscriber information sometimes. Sometimes the number fluctuates, sometimes is just plain drops off.
Matt Shobe also provided some pointers:
As for the Google Reader numbers disappearing; that's typically a temporary issue which finds Google not reporting the entirety of subscriber totals they've tallied on their end to us; as we have seen in other cases to date, this problem usually resolves itself within a day or two, and your totals return to their former levels. It is highly unlikely a mass unsubscription took place.
While this issue is personally frustrating (a blog is like a garden you are nurturing but for which you can only watch through a telescope - now you find that the telescope isn't working!) it points to a larger problem with the blogosphere: there are no market pressures to make monitoring of this type accountable. I see it as being in Google's court to figure out and communicate what is going on here. However, Google doesn't owe me or FeedBurner anything in this as they are freely contributing.
In terms of monitoring social media, I've believed for a long time that one can't take a single signal from content consumers (as, for example, Technorati does for its authority measure and blog ranking). The solution to computing and tracking 'influence' requires a complex of many signals which may contain redundancy of a kind but which will be more robust to failures of this type.