An alternative approach is to follow the simplifications made in the higherlevel user-interface building tools (see Chapter 5). Instead of dealing with
atomic-level features, why not create a model based on the widgets (interface
components) supported in the tool? Once a scrolling-list widget was tested to
determine user performance as a function of the number of items and the size of
the window, the performance of future widget users could be predicted auto-
matically.