Predicting the skilled use of hierarchical menus with the keystroke-level model

This article addresses a key question in the application of Card, Moran, and Newell's (1983) keystroke-level model to software in which users specify a command by working through a system of hierarchical menus. For example, to insert a row in Lotus 1-2-3®, the user makes three menu choices: W for worksheet, I for insert, and R for row. In the keystroke-level model, it is assumed that a time-consuming mental operation precedes each command. The question in the application of the keystroke-level model to hierarchical menu systems is whether the keystrokes WIR in the previous example constitute the execution of three commands and thus require three mental operations or whether WIR acts as a single command and requires only one mental operation. Data were collected from four highly experienced Lotus 1-2-3 users as they went about their day-to-day work. Strong evidence that only one mental operation is involved in choosing from a hierarchical menu system was obtained. We hypothesize that the discrepancy of our results from the data of others is due to the fact that our subjects were more experienced. The implications of our findings for the design of menus is discussed.