BNP vs Obama: stats lesson

I posted about how Hitwise blogger Robin Gould was noting the large number of searches for Obama information (I actually said Heather Hopkins, sorry Robin) from the UK.

This clanged for me because a think tank, the Centre for Policy Studies, publicised numbers last month, sourced from Hitwise, that the BNP had the most popular UK political party website.

So I asked them wassup? and they responded:

Last year we did issue a statement about BNP and CPS are quoting correct information that BNP were the most visited party website at the time of the release. Please do bear in mind our data is referring to percentage of site visits and not unique visitor numbers.

Here's the difference:

Unique Visitors: Represents the number of unduplicated (counted only once) visitors to your website over the course of a specified time period. A Unique Visitor is determined using cookies.

Visits: How many new and returning visitors came to your site

Visits counts every single 'hit', whereas 'unique visitors' counts everyone who can be individually identified with the rider that they have cookies 'enabled'. So 'unique visitors' is the closest to actual visitor numbers.

The 'discount' for those who turn off cookies is a guess but would be fairly small - maybe 2%? - in the general population. Reviewing my blog stats, which come from three sources, this explains the differences I see there (my blog is more likely to have visitors who deliberately turn off cookies, which could be tekkies or, from another angle, gay Egyptians).