Fig. 2.

Screenshot of the “Know Addiction” app user interface, which displays the time spent on each app. This is a screenshot of the “Know Addiction” app user interface from a problematic smartphone user. This app operates in the background and records the screen-on and screen-off timestamps of each app, thus measuring usage. The upper part of the screenshot shows the five most-used apps of the previous day (March 19), including the total duration and proportion of each app use. The lower part of the screenshot shows the five most-used apps of the past four weeks-long period (February 21 to March 19), including the total duration and proportion of each app use. The most-used apps on March 19 were somewhat different from the ranking of the past four months-long period (February 21 to March 19). The third to fifth most-used apps on March 19 were Youtube, Instagram, and Messenger, respectively, while the third to fifth most-used apps over the previous month were Messenger, Youtube, and Instagram, respectively, which reveals fluctuations in mobile apps' usage