  In recent years, European regulators have debated restricting the time an
online tracker can track a user to protect consumer privacy better. Despite the
significance of these debates, there has been a noticeable absence of any
comprehensive cost-benefit analysis. This article fills this gap on the cost
side by suggesting an approach to estimate the economic consequences of
lifetime restrictions on cookies for publishers. The empirical study on cookies
of 54,127 users who received 128 million ad impressions over 2.5 years yields
an average cookie lifetime of 279 days, with an average value of EUR 2.52 per
cookie. Only 13% of all cookies increase their daily value over time, but their
average value is about four times larger than the average value of all cookies.
Restricting cookies lifetime to one year (two years) decreases their lifetime
value by 25% (19%), which represents a decrease in the value of all cookies of
9% (5%). In light of the EUR 10.60 billion cookie-based display ad revenue in
Europe, such restrictions would endanger EUR 904 million (EUR 576 million)
annually, equivalent to EUR 2.08 (EUR 1.33) per EU internet user. The article
discusses these results' marketing strategy challenges and opportunities for
advertisers and publishers.
