The collected measurements may be unable to detect the impact of minor site changes, such as the change of a link’s text colour from blue into red. Finally, these studies are often too costly and may even lead to negative side effects (how would you feel if your preferred supplier asks you for the third time this week to fill in a survey?). For these reasons, combined with the availability of clickstream data, practitioners tend to prefer web metrics based on clickstream data. The evolving use
of this category of web metrics is the topic of the first part of this section; in the second part we focus on the limitations of clickstream data