Scott Whitney had a question for us regarding the number of downloads of your RSS (XML) file versus the number of downloads of the actual audio file (Podcast) identified within it:

Do you have any data regarding the normal ratio between number of feed downloads (the XML file) versus the actual number of audio downloads? And, any explanation why there would be a measurable difference?

Our response covers a couple of the many reasons why it will be different:

The number of downloads of the XML file versus the audio file is almost always very different, for several reasons. In a perfect world, all RSS aggregators would make use of the feature in which the aggregator asks the web server “Has this feed changed since I last downloaded it at time X ?”. If there was no new audio program in the feed, the server would respond “No”, and the XML file would not be downloaded. Only when there was a new post/program would the XML file be downloaded, as would the audio file, and there would be a 1:1 ratio between the two.

However, many aggregators do not use this feature, and just blindly pull the XML file every time, new or not. This, coupled with the fact that most aggregators can be changed by the user as to how often they check the XML file (anywhere from every minute to once a day), leads to the XML file being downloaded many more times than the audio file itself. Also, things like people opening the XML file in a browser, etc., lead to many more hits on the XML file than the audio.

I don’t have any hard data on the ratio of XML versus audio downloads, because it is all over the map depending on which podcast, time-period, etc. is looked at.

On a related note, inferring subscriber statistics from the number of hits on the XML file is very inaccurate, because of the same reasons. The number of downloads of the audio file itself is more accurate, but still not completely accurate, because of multiple downloads of the file by the same aggregator/person (more downloads than real subscribers), and services like iTunes and Odeo that cache your audio file for their users (less downloads of the file from your server than actual subscribers).