NPR vs. PBS web traffic

I've been seeing more and more Alexa web traffic graphs inserted in various blog postings, so thought I'd play with it.  The graph inserted here compares NPR.org (Alexa rank 1,197) with PBS.org (Alexa rank 1,077) for the past 12 months.  In the broadcast world, NPR stations have roughly four times more listening per user than PBS stations have viewing per user, giving public radio double the contact hours per year.  On the other hand, public television's cumulative (sampling) usage is roughly triple that of public radio's.  Alexa's daily reach statistic is a cumulative metric, so the fact that they're this close probably says something about public radio's audience being more webcentric than public television's audience.  Also, it's interesting to see how episodic PBS.org is over time -- apparently program-driven.

For a local station comparison, here's a graph comparing the two major public stations in New York, WNET-TV (Alexa rank 68,256) and WNYC-FM (Alexa Rank 30,389).

Click images to enlarge.

Update 9:35p Pacific Time.  Be sure to read Bob Lyons' methodology comment below.  Alexa's metrics come from monitoring attention from users (all using Internet Explorer) of its toolbar.  The company has a page describing its methodology from which comes the following quote:

... the Alexa user base is only a sample of the Internet population, and sites with relatively low traffic will not be accurately ranked by Alexa due to the statistical limitations of the sample. Alexa's data come from a large sample of several million Alexa Toolbar users; however, this is not large enough to accurately determine the rankings of sites with fewer than roughly 1,000 total monthly visitors. Generally, Traffic Rankings of 100,000+ should be regarded as not reliable because the amount of data we receive is not statistically significant. Conversely, the more traffic a site receives (the closer it gets to the number 1 position), the more reliable its Traffic Ranking becomes.

  --Dennis.  Alexa rank 532,641 ;-).   Technorati rank 80,433  :-o

Comments

[blyons]

i've been getting rapture of the stats with alexa for some time now.

i agree with your reading of these.

but i have a question about the methodology--how skewed a sample does alexa rely on--is it alpha geeks with
the alexa plug in on their browser?

that would be a significant skew

but even if so, the skew could be very useful as it would (arguably) be tilted towards future usage (as these folks are the pioneers)
bl