Problogger interviews Feedburner’s Rick Klau about why Feedburner readership counts vary so much. Here’s the answer to that burning question:

The fluctuations are almost always due to people using stand-alone computers who don’t turn their computer on, or don’t load their feed reader on a given day. If their feed reader doesn’t ask for the feed that day, we don’t see them, and consequently don’t include them as a subscriber. (note from Darren - this is why on weekends numbers tend to go down as a result of less people checking their feed reader).

Klau mentions a study they did last year of TechCrunch subscribers which looks at how they measure subscriber count and what’s not included.

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