Keystroke-Level Model

IST 331Gaurav Dubey

Based on ‘The ABCs of Users’, Ritter et al 2011

Keystroke-level model

• Simplified version of GOMS• Fast, approximate way to calculate time taken

to complete a task• Assumptions– Simple world– Single-tasking– No interruptions– Single method to complete a task

Characteristics

• No need to worry about goals or selection rules• Easier to use, but more limited applicability• Can be improved by incorporating Fitts’ Law,

and by using tables for keystroke speeds for individual keys

Operators

• Keystrokes (K): 0.08s to 1.2s per keystroke, mouse click, or button press

• Pointing (P): 1.1s (or as determined using Fitts' Law) for moving mouse to target

• Homing (H(mouse) or H(keyboard)): 0.4s for moving hand between mouse and keyboard

• Drawing (D): 0.9n + 0.16l where n = number of segments, l = total length of segments

Operators

• Mental operators (M): 1.35s to think about task– These should be placed between all operators

EXCEPT those linked through knowledge or skill (essentially, they should be placed between complete "cognitive units")

• System response time (Sys): as estimated based on system