Watch out, Feedburner's numbers are woefully inaccurate! … but why?

This was Rand's response to a comment I made about Rand's confirmation of Aaron's claim that an RSS subscriber is worth 1000 links.

Here is my comment:

Wed (6/27/07) at 07:38 AM

Very useful links. I really like the Adwords tip.

An RSS Subscriber is Worth a Thousand Links – well said, Aaron, and very true (though I'd say, rather, 250 or 300)

I think it all depends on the quality of the links, the content on your blog, and your audience.

I checked some A-list blogs to compare subscribers count and inbound links:

SEOmoz

13,109 subscribers

998,000 links

76.13 links per subscriber

Problogger

25,579 subscribers

543,000 links

21.23 links per subscriber

Copyblogger

19083 subscribers

196,000 links

10.27 links per subscriber

Shoemoney

9737 subscribers

127,000 links

13.04 links per subscriber

John Chow

5,818 subscribers

127,000 links

21.83 links per subscriber

The gap doesn't seem to be so big.

What got me intrigued was the fact that bloggers are losing credibility on Feedburner's ability to accurately count RSS subscribers. I noticed, especially on Seomoz that RSS subscriber numbers jump up and down drastically, usually during weekends.

We all like to see our reader stats, count and traffic as a measure of whether we are doing things right or wrong. When WordPress.com dropped the RSS stats tab, they motivated me to host my blog on this server. I am glad they did as I have a lot more flexibility now. I will write a post with more details on the move soon.

I decided to dig deep for clues as to how Feedburners assess the subscriber count. I had the feeling they were measuring the hits to the RSS pages. But, how they account for the hits coming from aggregator services like Bloglines, Google Reader, etc was the question.

How Feedburner estimates the number of RSS readers?

If you are a regular reader, you already know that I love to read cryptic log files. Here is another example where they come in handy.

I looked in this blog's log file for hits from the RSS feed aggregators such as Google Reader and MyYahoo!. I didn't need to look any further.

Here are a couple of fresh log entries:

72.14.199.66 – – [27/Jun/2007:15:06:47 -0400] "GET /feed/ HTTP/1.1" 304 – "-" "Feedfetcher-Google; (+http://www.google.com/feedfetcher.html; xx subscribers; feed-id=xxxxxxxxxxxxxxxxxxx)" "-"

209.131.41.49 – – [27/Jun/2007:13:08:43 -0400] "GET /feed/ HTTP/1.0" 200 63041 "-" "YahooFeedSeeker/2.0 (compatible; Mozilla 4.0; MSIE 5.5; http://publisher.yahoo.com/rssguide; users xx; views xxx)) " "-"

As you can see, these services report the number of subscribers in the HTTP_USER_AGENT field. Feedburner only needs to extract that information and voila. There is the magic.

How trustworthy is that information?  How is it generated?

From http://publisher.yahoo.com/rss_guide/faq.php

Yahoo! generates approximate stats for the number of active subscribers and pageviews for your feed, based on a 30-day rolling average.

From http://www.google.com/help/reader/publishers.html

… Google Reader reports subscriber counts when we crawl feeds (within the "User-Agent:" header in HTTP). Currently, these counts include users of both Reader and iGoogle; over time they'll alsol include subscriptions from other Google properties.

This means that the accuracy of Feedburner depends heavily on the accuracy of the information provided by the aggregators. It might not be completely accurate but my bet is that it is far better than nothing. WordPress.com bring the Feed Stats back!

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