On-site Versus Off-site Web Analytics – 2. How They Work

This is a edit of an article I originally wrote for journalism.co.uk to discuss what digital data
is accurate (and what is not) from a publisher’s point of view.

Part ONE:

  • Most of the web is junk, but web analytics can help
  • The two types of web analytics
  • The accuracy debate: On-site versus off-site metrics

Part TWO (this page): On-site and off-site analytics tools – how they work

Part THREE: On-site versus off-site analytics tools – what’s accurate?

How off-site web analytics works

Off-site web analytics tools measure your potential website audience. They are the macro tools that allow you to see the bigger picture of how your website compares to others. There are two types of techniques that achieve this:

  • Using panel data, or
  • Using Internet Service Provider (ISP) data

Using Panel Data

Companies such as comScore and Nielsen Netratings use the panel method by recruiting participants using a combination of their website and the calling of prospective panellists. Their technique is to have monitoring software installed on users’ computers to measure their web activity.

Panel sizes vary, but range from a few thousand, to hundreds of thousands of participants, with the majority of these based in the US. For example, comScore reports 2 million participants worldwide with over 50 per cent of these based in the US. Most panel participants are home users, as these are not restricted by IT policies when it comes to installing tracking software (public access is screened out from comScore data). Similar to election polling, panel data is extrapolated (multiplied up) to provide an estimate of the behaviour for total web population.

An important advantage of panel data is that the analytics vendor knows who its panellists are. Valuable demographic information such as age, gender, ethnicity, income bracket etc. are available. The caveat to this method, is that websites you wish to measure must have sufficient visitors to show up above the ‘noise’ threshold and mitigate sampling errors. Think of this in terms of having a high signal to noise ratio. The threshold will vary depending on where most of your visitors connect from, as the sample size of panellists varies from country to country.

Using Internet Service Provider (ISP) data

As an alternative to user panels companies such as Hitwise (part of Experian), collect off-site visitor information by aggregating anonymous data provided by ISPs. This has the potential to offer much larger sample sizes than panels (Hitwise reports 25 million people worldwide, 40 per cent based in the US) and therefore a lesser degree of extrapolation is required, potentially resulting in greater accuracy.

Because this type of off-site tracking happens at the ISP/network level, all visitor types are represented, including home, work, mobile, educational and public access. The trade off is that this data is anonymous. Therefore demographic user data is not available.

How on-site web analytics works

On-site web analytics tools measure the actual visitor traffic arriving on your website. Examples include Google Analytics (which dominates the market place), Adobe Site Catalyst, WebTrends etc. They are capable of tracking the engagements and interactions your visitors have. For example, whether they convert to a customer or lead or not, how they got to that point (or where they dropped out), what they purchased and how much they spent, what campaigns they viewed and clicked on, and so forth.

Although there are several techniques to measure visitors on your site, the method used by the vast majority of vendors is the so-called ‘page tagging’ technique. This requires the placement of a small snippet (aka ‘tag’) of JavaScript code on your web pages that act as a beacon – capturing visitor information, storing these as cookies, then broadcasting this to data collection servers in real-time.

Access to data is different for each

A key difference between on-site and off-site web analytics tools is that on-site visitor data is only available to the website owner and the people he/she grants access to. Conversely off-site web analytics data can be obtained for any website – that is, you own website and your competitors – provided there is sufficient visit data.

…continue to Part THREE: “On-site versus off-site analytics tools – what’s accurate?”


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