Subscriber number accuracy (or the myth of the fluctuating daily subs)

[Reid]

I wanted to start a discussion about the daily fluctuating
subscribers. The standard line from Feedburner is that they can only
count a subscription when someone opens their feed reader, so that the
reason that your subscriber numbers fluctuate from day to day is
because some people will open up their feed readers on one day and not
another.

However, after looking at the "Feed Readers" stats for all of the
feeds that I manage, this does not seem to be the case. The number of
subscribers for Google Feedfetcher and Bloglines will always stay the
same (or rise with new subscriptions), whereas the fluctuating numbers
come mostly from Mozilla, "Java-based reader" and "Other readers".

Therefore, the problem does not seem with subscribers not opening
their readers on given days, but rather Feedburner's inability to
completely track subscribers.

A little background: I manage a couple of dozen feeds through
Feedburner, the smallest of which averages about 18 subscribers and
the largest just over 1,000. In all of these, the subscriber numbers
fluctuate pretty wildly from day to day, but the Google Feedfetcher
and Bloglines subscribers never change except when new subscribers
come in, at which point they keep that new, higher number. But they
don't fluctuate at all. In that ~18 subs feed that I mentioned, it's
fluctuated between 15 and 22 in recent weeks, but there's *always* ten
subscribers using Google Feedfetcher and there's *always* one
subscriber using Bloglines, even on the weekends. Meanwhile, the rest
of the subs fluctuate wildly.

I really like the Feedburner service and I don't plan on not using it,
but I'm getting concerned about how accurate the numbers are.
Clearly, the "it depends on if subscribers open their feed readers"
reasoning for fluctuating subscribers doesn't hold up, as it seems to
depend much more on which kind of feed reader they're using rather
than whether they open it or not.

It would be great to hear from an employee of Feedburner on this
issue: why are statistics for some feed readers accurate and some
not? And if this is the case, couldn't Feedburner split the users
into "known" (ie accurate) and "unknown" (possibly not accurate)? For
non Feedburner employees: has anyone else found the same thing?

[deewreck]

Yea, like Reid, I'd like to get some feedback regarding the
fluctuation of my subscribers in numbers from day to day. It is a
little confusing. I'm new to blogging and so I'm trying to get an
understanding as to whether my blog is increasing its subscriber base.
With the number of subscribers fluctuating daily I'm not able to
determine this. More insight on how I'd be able to do this with
Feedburner would be great.

Thank you in advance.

Derrick