Alexa data: how accurate is it – using audited ABCe figures to check?
Alexa.com lets you compare stats about websites. But how representative is its data? It's hard to know as it gives figures as %s rather than absolute numbers.
So, to find out, I've compared Alexa with the ABCe official audited data for UK newspaper sites - using the figure for the %age of each site's visitors from the UK.
As the table shows, Alexa is good but not brilliant.
Alexa vs ABCe
|Newspaper||Alexa: UK as % of total||ABCe: UK as % of total|| Margin of error
In particular, Alexa consistently underestimates the proportion of users who are from the UK (maybe reflecting its American roots?). However, the Mirror apart, the spread of errors is reasonably consistent.
Using the table:
- Clicking the first column takes you to the relevant Alexa page.
- The Alexa column shows the percentage of users Alexa thinks come from the UK. They don't give the timeframe.
- For the ABCe column, I dividing the June ABCe figures for total unique UK users into the overall total unique users. The FT isn't shown as it isn't audited every month (and wasn't in June). The Express's site isn't audited. The ABCe do some aggregating of data - for instance, the Sun figure includes the News of the World site. Alexa treats this separately.
- The average is a simple average - it isn't weighted in any way.
Using Alexa data
I'm going to use Alexa to make more comparisons about UK newspapers over the next few days.
You can read more about interpreting Alexa data on Alexa's own explanatory page - in particular note that they no longer just rely on people who have downloaded their toolbar, as they did in the past.
Some other information about the data (but much of it written when they did still rely on ONLY the toolbar data) includes:
- Impact of Museum Websites - a comparison using Alexa (see the comments)
- Please stop quoting Alexa data (although see the last comment where the author says things have improved).
- Alexa toolbar and the problems of experiment design.
- And Mark Pack's recent post (March 2010) on how the internet is changing British politics (well worth a read).