What is the Keystroke Level Model (KLM)?

The Keystroke Level Model studies human computer interaction in an effort to improve the performance and usability of a site by analyzing how users interact with it. By modeling user behavior, estimates can be made about how long it takes to achieve certain tasks and what can be done to improve efficiency.

The questions KLM aims to answer?

• Can users complete the tasks / goals of the site?
• Can users complete the tasks within a reasonable amount of time and with minimal errors?
• Can novice users learn how to complete tasks within a reasonable time?

How does KLM answer these?
The sequence of steps to complete a task, such as completing an online form, is identified. Each operation is then assigned a duration to estimate how long it would take a user to perform, with different estimates available for novice and advanced users. By defining each step and associated time, unnecessary or redundant tasks can be identified and removed to improve the efficiency and usability of a site.

The following formula is used to calculate the keystroke model:
By listing the sequence of tasks (operators) you can assign estimations for each and then totaling the list gives you the total time needed to complete the task.

The following lists the standard operators and average times for each:

• K, key press and release (keyboard) - 0.28 sec
• P, point the mouse to something - 1.1 sec
• B, button press or release (mouse) - 0.1 sec
• H, hands movement from mouse to keyboard or reverse - 0.4 sec
• M, mental thinking - 1.2 sec
• W, wait time (system) - t msec

Example of a KLM calculation:
Task: Users searches for word using search bar

1. Reach for Mouse = H = 0.40 seconds
2. Move pointer to Search bar = P = 1.10 seconds
3. Click in search field = K = 0.28
4. Hand moves to keyboard = H = 0.40 seconds
5. Think of word to be searched for = M = 1.20 seconds
6. Type word in search field = 8 x K = 2.24 seconds
7. Reach for mouse = H = 0.40 seconds
8. Move pointer to ‘Go’ button = P = 1.10 seconds
9. Click on ‘Go’ button = K = 0.28 seconds
10. Wait for search results to appear = W = 1.25 seconds

Total Time to complete this task is 8.65 seconds

In summary, KLM provides designers with a method of analyzing task executions so that alternative methods can be reviewed to find the best and most efficient way to execute website activities.