Scroll Event

A scroll event is recorded when the user scrolls down a page, usually at threshold points like reaching 25, 50, 75 and 100 percent of the page.

A scroll event is the raw material for measuring how much of a page was seen and is the basis of the scroll map and scroll depth. An important design point is that raw scrolling fires at high frequency, and if every pixel of movement becomes an event it both chokes the network and renders the data useless; so it is usually limited to a few percentage thresholds to keep the signal meaningful. The interpretive trap is that scrolling to the end is not the same as reading: a user can whip to the bottom without reading anything, so a scroll event alone does not establish attention and is better paired with active time. The second point is page-height dependence: 50% scroll on a short page and a very tall page means two completely different amounts of content, so comparing depth across pages of different length must be cautious.