KLM (human-computer interaction)

In human–computer interaction, the keystroke-level model (KLM) predicts how long it will take an expert user to accomplish a routine task without errors using an interactive computer system. It was proposed by Stuart K. Card, Thomas P. Moran and Allen Newell in 1980 in the Communications of the ACM and published in their book The Psychology of Human-Computer Interaction in 1983, which is considered as a classic in the HCI field. The foundations were laid in 1974, when Card and Moran joined the Palo Alto Research Center (PARC) and created a group named Applied Information-Processing Psychology Project (AIP) with Newell as a consultant aiming to create an applied psychology of human-computer interaction. The keystroke-level model is still relevant today, which is shown by the recent research about mobile phones and touchscreens (see Adaptions).

The keystroke-level model consists of six operators: the first four are physical motor operators followed by one mental operator and one system response operator:

Use Rule 0 to place candidate Ms, and then cycle through Rules 1 to 4 for each M to see whether it should be deleted.

Place Ms in front of all Ps that select commands (not arguments).

The following table shows an overview of the times for the mentioned operators as well as the times for suggested operators:

Guidelines:
.08 (135 wpm: best typist)
.12 (90 wpm: good typist)
.20 (55 wpm: average skilled typist)
.28 (40 wpm: average non-secretary typist)
.50 (typing random letters)
.75 (typing complex codes)
1.20 (worst typist and unfamiliar with the keyboard)

The KLM is based on the keystroke level, which belongs to the family of GOMS models. The KLM and the GOMS models have in common that they only predict behaviour of experts without errors, but in contrast the KLM needs a specified method to predict the time because it does not predict the method like GOMS. Therefore, the KLM has no goals and method selection rules, which in turn makes it easier to use. The KLM resembles the model K1 from the family of GOMS models the most because both are at the keystroke level and possess a generic M operator. The difference is that the M operator of the KLM is more aggregated and thus larger (1.35 seconds vs. 0.62 seconds), which makes its mental operator more similar to the CHOOSE operations of the model K2. All in all, the KLM represents the practical use of the GOMS keystroke level.

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