Blog

Cookie Length

Many tracking tools set cookies for 90 days. This is crucial for verticals with long consideration periods before purchase. Travel is the prime example - consumers might research a holiday destination over the Christmas period, but not book until much later in the year. Car insurance is another example, where consumers research ahead of their renewal date.

However some sites set them for a short period - one week, for example. This may be because they do not want to pay affiliates for repeat visitors making repeat purchases (for the affiliate angle on this, see this blog post). Or it may be the site owner thinks consumers normally buy within 7 days and if they return after that period they can be viewed as a "new" visitor motivated by brand loyalty or other adverts. Ideally different traffic sources should have different cookie lengths set.

Personally I think 7 days is too short in most situations - what if the consumer needs to wait after payday and bookmarks the site until then, or are researching a gift for a relative and have a longer consideration time to buy? 14 or 30 days seems more appropriate.

Repeat conversion window and view conversion window are two other important settings to consider with ad tracking tools.

The former ensures that if a consumer clicks twice on the buy button - e.g. because their connection is slow - conversions aren't double-counted when in fact there is only one sale. An example setting is one minute.

View conversion window determines the time frame in which conversions are recorded after a view of a banner; so if this is set to 14 days and a consumer visits the site without viewing/clicking any other ad link and completes a tracked action within 14 days, then that banner receives the credit for the conversion. This opens up a discussion on first click vs last click conversion tracking, but I'll save that for another day...

Advanced Reporting and Cookies

There's another problem with setting short cookie lengths - one which may grow. As tracking tools provide more visibility on the overall path of a consumer - which banner ads they saw/clicked on, which PPC ads they clicked on, which natural search links they clicked on, which emails they viewed/clicked on, and which affiliate links they clicked on - so the cookie length becomes more important. Consumers will typically be exposed to these different ads and their tracking links over a longer period of time than if the tracking tool and cookie only recorded data from one type of campaign. If the cookie length is too short, E2C (Dart) and Engagement Mapping (Atlas, now MS Advertiser and Publisher Solutions) will be next to useless.

Ideally, reports should use long-length cookies and record first visit, second visit etc so site owners know their volume of repeat visitors as well as truly new ones, the buy rates of both, and the ads they saw/clicked on along the way - providing enhanced visibility, leading to more informed buying decisions.

Analytics vs Tracking

The above "ideal" ad reporting blurs the line between analytics packages and tracking solutions. To my mind, the two can be defined as:

Ad Tracking (Atlas, Dart etc) - these solutions track adverts that lead visitors to the website, and may then record if they complete a defined action (like a sale or email subscription). They only work for sources of traffic where the URL can be controlled to use a redirect URL or have a code appended to the end, resulting in the visit source being recorded and a cookie dropped during redirect or by the destination site.

Analytics (Google Analytics, Webtrends etc) - these packages record all site traffic, can determine its source of URLs are tagged up accordingly, and record site activity - not just sales or similar actions, but also page views, visit lengths etc.

All too often, these two sets of tools create silos of overlapping, sometimes contradictory data. We often have clients ask why tracking tools produce different numbers to their analytics software. Cookie length is one factor - followed by different counting methods, de-duplication, JavaScript availability, browser security settings, conversion window settings, 1st vs 3rd party cookies etc.

So, cookie length is important - and needs to be seen in the wider context of the convergence of analytics and tracking solutions (an end to data silos!) alongisde the mergence of advanced reports. Especially now that Google and Microsoft both own ad tracking and serving companies, search engines, display ad networks and analytics packages...I think report convergene may be a hot topic in the later half of 2008 and into 2009.