What metrics have been used differentiate between user engagement and addiction?

There have been some recent press about the computer game Fortnite that has caused concern for parents of children that are spending excessive time playing due to its seemingly addictive effect on players (many of whom are young children).

Most of the design patterns and interactions built into games and applications with a focus on entertainment is aimed at increasing engagement, which is often inferred from the amount of onscreen time. While it can be easier to work out the difference between engagement and addiction using more qualitative methods, the behavioural patterns between an engaged vs. addicted user might be harder to determine using quantitative methods.

Is it assumed that engagement precedes addiction, and if so then is it possible to measure the behavioural change over time to identify at risk users?

If engagement and addiction are completely different behaviours, what are the differences that allows you to distinguish one group from the other?