Cookies are small text files used to store information on user computers’ local
hard drives. They fall into two broad categories — transient and persistent.
A transient cookie is one that is created at the start of every session and deleted at the end
of the session.
A persistent cookie, on the other hand, outlasts the user session. It is created when the user
first enters the server’s website and is updated each time the user re-enters the site using the same computer.
Cookies are primarily intended to improve the user’s on-site experience. For instance, cookies can store
information to allow users to re-enter sites without having to login. The stored data usually includes unique user IDs
and user preferences.
Cookies are also used for tracking of users via their devices and for collecting
and reporting usage statistics. Analytics platforms often rely on cookies to track usage behaviour
on websites without personally identifying individual visitors.
Exhibit 28.5 Deletion of cookies inflates user count (source: Lessons learned in Digital Advertising,
comScore).
A common method of tracking “New” and “Repeat” users
is via persistent cookies. This approach however suffers from numerous drawbacks.
Users periodically delete cookies. When they do so, there is no way of identifying them by their original ID.
On return to the site, they are assigned a new ID, and counted as new users. . This, according to ComScore (Exhibit 28.5),
can exaggerate user count by 2.5 to 3 times. The analytics firm estimates, in Asia Pacific, 30 to 40% of net users delete
cookies, as often as 4 to 5 times per month.
Moreover, cookies only count devices, not people. If a user accesses a site
from various devices, either owned or shared, they are counted multiple times, inflating the new
user count and deflating the repeat user count. Some users also disable cookies, and cookies can
become outdated, although this is not a major concern since the proportion of users who disable
cookies is small.
