Keystroke-level model: Difference between revisions

Revision as of 12:35, 5 July 2015

Revision as of 12:37, 5 July 2015

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== Example Calculation==

The following example slightly modified to be more compact from Kieras shows the practical use of the KLM by comparing two different ways to delete a file for an average skilled typist. Note that M is 1.35 seconds as stated in the KLM<ref name="klm-paper-operators-table" /><ref name="klm-book-operators-table" /> instead of 1.2 seconds used by Kieras. The difference between the two designs would remain the same either way for this example.

{| class="wikitable"

Change the code in Line 512 from "hte" to "the" ('the'the' in computer language) and then press Enter Key

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! Design A: drag the file into the trash can<ref>{{cite web|last1=Kieras|first1=David|title=Using the Keystroke-Level Model to Estimate Execution Times|url=http://www-personal.umich.edu/~itm/688/KierasKLMTutorial2001.pdf|accessdate=22 June 2015|ref=31|page=3}}</ref> !! Design B: use the short cut “control + T”<ref>{{cite web|last1=Kieras|first1=David|title=Using the Keystroke-Level Model to Estimate Execution Times|url=http://www-personal.umich.edu/~itm/688/KierasKLMTutorial2001.pdf|accessdate=22 June 2015|ref=31|page=6}}</ref>

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| method encoding (operator sequence)<ref>{{cite web|last1=Kieras|first1=David|title=Using the Keystroke-Level Model to Estimate Execution Times|url=http://www-personal.umich.edu/~itm/688/KierasKLMTutorial2001.pdf|accessdate=22 June 2015|ref=32|page=9}}</ref>|| method encoding (operator sequence)<ref>{{cite web|last1=Kieras|first1=David|title=Using the Keystroke-Level Model to Estimate Execution Times|url=http://www-personal.umich.edu/~itm/688/KierasKLMTutorial2001.pdf|accessdate=22 June 2015|ref=33|page=10}}</ref>

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# initiate the deletion (M)

# find the file icon (M)

# point to file icon (P)

# press and hold mouse button (B)

# drag file icon to trash can icon (P)

# release mouse button (B)

# point to original window (P)

||

# initiate the deletion (M)

# find the icon for the to-be-deleted file (M)

# point to file icon (P)

# press mouse button (B)

# release mouse button (B)

# move hand to keyboard (H)

# press control key (K)

# press T key (K)

# move hand back to mouse (H)

|-

| Total time || Total time

|-

| 3P + 2B + 2M = 3*1.1 sec + 2*.1 sec+ 2*1.35 sec = 6.2 sec || P + 2B + 2H + 2K + 2M = 1.1 sec + 2*.1 sec + 2*.4 sec + 2*.2 sec + 2*1.35 sec = 5.2 sec

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This shows that Design B is 1 second faster than Design A, although it contains more operations.

or

" Change 512 'hte'the' "

'''Steps'''

*Mentally prepare

*6 average speed keystrokes (for word "change")

*1 average speed keystrokes for space bar

*3 keystrokes for pressing numbers "512"

*1 average speed keystrokes for space bar

*Mentally Prepare by reading what needs to be changed

*6 average keystrokes for typing {{Not a typo|hte}} and the

*3 keystrokes to press the 3 " ' "

*1 keystroke to press Return Key

'''Values'''

K1 = average speed keystrokes (0.20 seconds)

K2 = typing random letters (0.50 seconds)

M = Mentally Prepare (1.35 seconds)

Put above steps into formula: M + 6K1 + K1 + 3K2 + K2 + M + 3K1 + K2 + 3K1 + K2 '''=''' 2M + 14K1 + 6K2 = '''9.82 seconds'''

This method assumes that operator times are invariant and do not depend on the previous sequence of events. New physical operators can be added if their timing can be represented as a simple context-free function. KLM-GOMS does not account for either slips or mistakes automatically—the analyst must create separate models of error sequences and perform their own sensitivity analysis.

The placement of the keystrokes and pointer operations are straightforward, but the placement of the mental operations is not. Mental operations are placed by a set of rules that require some interpretation, such as determining a conceptual "cognitive unit" or grouping of actions. For instance, pressing ctrl and c simultaneously to perform a "copy" would be considered a single cognitive unit. Mental operations are inserted before each cognitive unit to account for cognitive preparation and decision-making.

The main reason a designer or analysts would use this technique is that it is a very fast. Different designs or systems can be compared against one another quickly. It does not require that the evaluator be an expert in GOMS because the procedure is an explicitly laid out recipe. A major caution is that the algorithm is designed to estimate the execution time for an expert user, which is typically faster than the time for a new user or an unfamiliar task.

== See also ==