How reliable is cookie-based tracking?

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The issue of the reliability of cookie-based tracking is perhaps one of the most important issues for publisher s and always has been.

Affiliate marketing operates on the basic assumption that the sales publisher s refer to advertisers are tracked and reported correctly.

It is helpful to think of two separate but linked aspects to the issue of reliability. Firstly, there are the technical aspects around the reliability of cookie-based tracking: what technologies are available and how reliable are they?

Second, there are user-based or privacy issues. These are related to technical issues but concern more precisely users’ understanding of how cookies are used and their possible motives for deleting them.

The technological reliability of cookie-based tracking in and of itself is pretty robust. Where technical problems in tracking occur they are far more likely due to a failure of the tracking on the advertiser’s site firing than to the cookie placed at the time of the user’s click.

In terms of the user-related aspects things are more complicated. Recent research by Specific Media indicates that the public attitude to the use of cookies is fairly relaxed. Users understand cookies are necessary to store preferences and details, and are comfortable that they are used to serve ads.

There is more concern around behavioural retargeting though, echoed at a supra-national level in the form of the EU’s ePrivacy Directive, something which will affect advertisers, publisher s and networks alike, and is therefore almost certainly the biggest industry-wide challenge that publisher marketing currently faces.

Examining in more detail how these dual aspects, technical and user-based, interact, it is helpful to distinguish between different types of cookies and look at their respective likelihoods of deletion.

Affiliate Window uses first party cookies set by the awin1.com domain and so are likely to suffer lower deletion rates than third party cookies set by third parties. The vulnerability of third party cookies varies by browser.

Safari automatically blocks third party cookies, as will certain plugins for other browsers, which could pose a problem for advertisers relying too heavily on certain third-party tracking solutions.

Web monitoring firm comScore has analysed cookie deletion patterns and in April 2010 reported that third party cookies were deleted by 30-40% of users and first party cookies were deleted at rates in excess of 20% (source).

This data however is not specific to the publisher channel and it is likely that users find certain other methods of cookie-based tracking more invasive and thus delete them.

In response to the implementation of the EU’s ePrivacy Directive behavioural re-targeters have implemented a button displayed in their ads which directs to a site offering users more information and the ability to opt-out. It is possible that UK publisher marketers might have similar recourse in the near future.

However, opting out and cookie deletion are two separate things. Opting out does not bear on the reliability of tracking methods in and of themselves; indeed, a persistent cookie has to be set on a user’s machine in order for an opt-out preference to be stored!

So what alternatives are available?

An publisher network should offer additional tracking methods for redundancy that can help reassure publisher s worried about high deletion rates. IP-based tracking, ETags and Flash cookies are some examples (more about these here) but on Affiliate Window these are necessary in only a small minority of cases.

Flash cookies have the advantage of tracking across different browsers (if a customer shops in IE but buys in Firefox, for example) and are stored separately to other cookies. Because the user has to go through a different process to remove these they are also less likely to be deleted.

Publishers that work on dual-network campaigns and have switched from one to the other have sometimes reported a mysterious change in the volume of sales they are producing. This might be an indication of the robustness of the different publisher networks’ tracking methods.

It has also been suggested that cookie deletion might be encouraged by some publisher s (notably, cashback sites) in order to minimise members’ transaction queries.

However, it is worth pointing out that at present neither of the two largest cashback sites prompt their users to delete cookies prior to clicking through to an advertiser, and do not appear to offer information on how to delete other publisher s’ cookies.

In conclusion, whilst the technological aspects of cookie-based tracking remain sound, in the current political climate following the adoption of the EU’s ePrivacy Directive the issue of how cookies are used is creeping closer to the forefront of public consciousness.

As the publisher industry like others adopts different methodologies to track and attribute sales transparency to users will be key in determining whether we witness a rise in opt-out and deletion rates.

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