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{{Short description|Form of 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.<ref>{{cite journal|last1=Card|first1=Stuart K|last2=Moran|first2=Thomas P|last3=Allen|first3=Newell|title=The keystroke-level model for user performance time with interactive systems|journal=Communications of the ACM|date=1980|volume=23|issue=7|pages=396–410|doi=10.1145/358886.358895|s2cid=5918086|ref=1|doi-access=free}}</ref> 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.<ref>{{cite web|last1=Sauro|first1=Jeff|title=5 Classic Usability Books|url=http://www.measuringu.com/blog/usability-books.php|website=MeasuringU|accessdate=22 June 2015|ref=7}}</ref><ref>{{cite web|last1=Perlman|first1=Gary|title=Suggested Readings in Human-Computer Interaction (HCI), User Interface (UI) Development, & Human Factors (HF)|url=http://hcibib.org/readings.html|website=HCI Bibliography : Human-Computer Interaction Resources|accessdate=22 June 2015|ref=8}}</ref> The foundations were laid in 1974, when Card and Moran joined the [[PARC (company)|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.<ref>{{cite book|last1=Card|first1=Stuart K|last2=Moran|first2=Thomas P|last3=Newell|first3=Allen|title=The Psychology of Human-Computer Interaction|date=1983|publisher=L. Erlbaum Associates Inc|___location=Hillsdale|isbn=978-0898592436|pages=ix–x|ref=4|url=https://archive.org/details/psychologyofhuma00stua}}</ref> The keystroke-level model is still relevant today, which is shown by the recent research about mobile phones and touchscreens (see [[#Adaptions|Adaptions]]).
== Structure of the
The
* '''K''' (keystroke or button press): it is the most frequent operator and means keys and not characters (so e.g. pressing SHIFT is a separate K operation). The time for this operator depends on the motor skills of the user and is determined by one
* '''P''' (pointing to a target on a display with a mouse): this time differs depending on the distance to the target and the size of the target,<ref>{{cite journal|last1=Fitts|first1=Paul M|title=The information capacity of the human motor system in controlling the amplitude of movement|journal=Journal of Experimental Psychology: General|date=1992|volume=
* '''H''' (homing the hand(s) on the keyboard or other device): This includes movement between any
* '''D''' (drawing (manually) n<sub>D</sub> straight-line segments with a total length of D(n<sub>D</sub>, l<sub>D</sub>) cm): where n<sub>D</sub> is the number of the line segments drawn and l<sub>D</sub> is the total length of the line segments. This operator is very specialized because it is restricted to the mouse and the drawing system has to constrain the cursor to a .56
* '''M''' (mentally preparing for executing physical actions): denotes the time a user needs for thinking or decision making. The number of Ms in a method depends on the knowledge and skill of the user. Heuristics are given to help decide where an M should be placed in a method. For example, when pointing with the mouse a button press is usually fully anticipated and no M is needed between both operators.<ref>{{cite journal|last1=Card|first1=Stuart K|last2=Moran|first2=Thomas P|last3=Newell|first3=Allen|title=The keystroke-level model for user performance time with interactive systems|journal=Communications of the ACM|date=1980|volume=23|issue=7|pages=
{| class="wikitable collapsible" border="1"
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* '''R''' (response time of the system): the response time depends on the system, the command and the context of the command. It is only used when the user actually has to wait for the system. For instance, when the user mentally prepares (M) for executing
The following table shows an overview of the times for the mentioned operators as well as the times for suggested operators:
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|-
| K || total typing test time/total number of non-error keystrokes<br />
Guidelines:<ref name="klm-paper-operators-table">{{cite journal|last1=Card|first1=Stuart K|last2=Moran|first2=Thomas P|last3=Newell|first3=Allen|title=The keystroke-level model for user performance time with interactive systems|journal=Communications of the ACM|date=1980|volume=23|issue=7|pages=399|doi=10.1145/358886.358895|s2cid=5918086|ref=5|doi-access=free}}</ref><ref name="klm-book-operators-table">{{cite book|last1=Card|first1=Stuart K|last2=Moran|first2=Thomas P|last3=Newell|first3=Allen|title=The Psychology of Human-Computer Interaction|date=1983|publisher=L. Erlbaum Associates Inc|___location=Hillsdale|isbn=
.08 (135 wpm: best typist)<br />
.12 (90 wpm: good typist)<br />
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| H || 0.4<ref name="klm-paper-operators-table" /><ref name="klm-book-operators-table" />
|-
| D || .9n<sub>D</sub> + {{not a typo|. 16 l}}<sub>D</sub><ref name="klm-paper-operators-table" /><ref name="klm-book-operators-table" />
|-
| M || 1.35<ref name="klm-paper-operators-table" /><ref name="klm-book-operators-table" />
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| colspan="2" | suggested operators
|-
| B (mouse button press or release) || 0.1<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=9|page=2|archive-date=19 March 2015|archive-url=https://web.archive.org/web/20150319195627/http://www-personal.umich.edu/~itm/688/KierasKLMTutorial2001.pdf|url-status=dead}}</ref>
|-
| Click a Link/ Button
|-
| Pull-Down List (No Page Load) || 3.04<ref name="sauro-suggested-operators" />
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== Comparison with GOMS ==
The KLM is based on the keystroke level, which belongs to the family of [[GOMS]] models.<ref>{{cite book|last1=Card|first1=Stuart K|last2=Moran|first2=Thomas P|last3=Newell|first3=Allen|title=The Psychology of Human-Computer Interaction|date=1983|publisher=L. Erlbaum Associates Inc|___location=Hillsdale|isbn=
== Advantages ==
The KLM was designed to be a quick and easy to use system design tool, which means that no deep knowledge about [[psychology]] is required for its usage.<ref name="klm-paper-advantages">{{cite journal|last1=Card|first1=Stuart K|last2=Moran|first2=Thomas P|last3=Newell|first3=Allen|title=The keystroke-level model for user performance time with interactive systems|journal=Communications of the ACM|date=1980|volume=23|issue=7|pages=409|doi=10.1145/358886.358895|s2cid=5918086|ref=19|doi-access=free}}</ref> Also, task times can be predicted (given the [[#Limitations|limitations]]) without having to build a [[prototype]], recruit and test users, which saves time and money.<ref>{{cite
== Limitations ==
The
* It measures only one aspect of performance: time,
* It considers only expert users. Generally, users differ regarding their knowledge and experience of different systems and tasks, motor skills and technical ability <ref name="klm-paper-limitations-users">{{cite journal|last1=Card|first1=Stuart K|last2=Moran|first2=Thomas P|last3=Newell|first3=Allen|title=The keystroke-level model for user performance time with interactive systems|journal=Communications of the ACM|date=1980|volume=23|issue=7|pages=397, 409|doi=10.1145/358886.358895|
* It considers only routine unit tasks <ref name="klm-paper-limitations">{{cite journal|last1=Card|first1=Stuart K|last2=Moran|first2=Thomas P|last3=Newell|first3=Allen|title=The keystroke-level model for user performance time with interactive systems|journal=Communications of the ACM|date=1980|volume=23|issue=7|pages=409|doi=10.1145/358886.358895|s2cid=5918086|ref=24|doi-access=free}}</ref>
* The method has to be specified step by step.<ref name="klm-paper-limitations" /> This makes it more accessible to use for an average person without advanced technical skills.
* The execution of the method has to be error-free <ref name="klm-paper-limitations" />
* The mental operator aggregates different mental operations and therefore cannot model a deeper representation of the user’s mental operations. If this is crucial, a GOMS model has to be used (e.g. model K2)<ref>{{cite book|last1=Card|first1=Stuart K|last2=Moran|first2=Thomas P|last3=Newell|first3=Allen|title=The Psychology of Human-Computer Interaction|date=1983|publisher=L. Erlbaum Associates Inc|___location=Hillsdale|isbn=
Also, one should keep in mind when assessing a computer system that other aspects of performance (errors, learning, functionality, recall, concentration, fatigue, and acceptability),<ref>{{cite journal|last1=Card|first1=Stuart K|last2=Moran|first2=Thomas P|last3=Newell|first3=Allen|title=The keystroke-level model for user performance time with interactive systems|journal=Communications of the ACM|date=1980|volume=23|issue=7|pages=
Furthermore, tasks which take more than a few minutes take several hours to model and a source of errors is forgetting operations.<ref>{{cite
In addition, the KLM can not make a perfect prediction and has a root-mean-square error of 21%.<ref>{{cite book|last1=Card|first1=Stuart K|last2=Moran|first2=Thomas P|last3=Newell|first3=Allen|title=The Psychology of Human-Computer Interaction|date=1983|publisher=L. Erlbaum Associates Inc|___location=Hillsdale|isbn=
== Example ==
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"
|-
! 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|archive-date=19 March 2015|archive-url=https://web.archive.org/web/20150319195627/http://www-personal.umich.edu/~itm/688/KierasKLMTutorial2001.pdf|url-status=dead}}</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|archive-date=19 March 2015|archive-url=https://web.archive.org/web/20150319195627/http://www-personal.umich.edu/~itm/688/KierasKLMTutorial2001.pdf|url-status=dead}}</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=32|page=9|archive-date=19 March 2015|archive-url=https://web.archive.org/web/20150319195627/http://www-personal.umich.edu/~itm/688/KierasKLMTutorial2001.pdf|url-status=dead}}</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|archive-date=19 March 2015|archive-url=https://web.archive.org/web/20150319195627/http://www-personal.umich.edu/~itm/688/KierasKLMTutorial2001.pdf|url-status=dead}}</ref>
|-
|
# 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
|-
|}
This shows that Design B is 1 second faster than Design A, although it contains more operations.
== Adaptions ==
The six operators of the KLM can be reduced, but this decreases the accuracy of the model. If this low of an accuracy makes sense (e.g. “back-of-the-envelope” calculations) such a simplification can be sufficient.<ref>{{cite book|last1=Card|first1=Stuart K|last2=Moran|first2=Thomas P|last3=Newell|first3=Allen|title=The Psychology of Human-Computer Interaction|date=1983|publisher=L. Erlbaum Associates Inc|___location=Hillsdale|isbn=978-0898592436|pages=[https://archive.org/details/psychologyofhuma00stua/page/296 296]|ref=34|url=https://archive.org/details/psychologyofhuma00stua/page/296}}</ref>
While the existing KLM applies to desktop applications, the model might not fulfill the range of mobile tasks,<ref>{{cite book|last1=Li|first1=Hui|last2=Liu|first2=Ying|last3=Liu|first3=Jun|last4=Wang|first4=Xia|last5=Li|first5=Yujiang|last6=Rau|first6=Pei-Luen Patrick|title=Extended KLM for mobile phone interaction: a user study result|journal=CHI EA '10 CHI '10 Extended Abstracts on Human Factors in Computing Systems|date=2010|publisher=ACM|___location=New York|isbn=978-1-60558-930-5}}</ref> or as Dunlop and Cross <ref>{{cite journal|last1=Dunlop|first1=M.|last2=Crossan|first2=A.|title=Predictive Text Entry Methods for Mobile Phones|journal=Personal Technologies|date=2000|volume=4|issue=2–3|pages=134–143|doi=10.1007/BF01324120|s2cid=194691|url=https://strathprints.strath.ac.uk/2580/6/strathprints002580.pdf}}</ref> declaimed KLM is no longer precise for mobile devices. There are various efforts to extend the KLM regarding the use for mobile phones or touch devices. One of the significant contributions to this field is done by Holleis, who retained existing operators while revisiting the timing specifications. Furthermore, he introduced new operators: Distraction (X), Gesture (G), Initial Act (I).
While Li and Holleis <ref>{{cite book|last1=Holleis|first1=P.|last2=Otto|first2=F.|last3=Hussmann|first3=H.|last4=Schmidt|first4=A.|title=Proceedings of the SIGCHI Conference on Human Factors in Computing Systems |chapter=Keystroke-level model for advanced mobile phone interaction |pages=1505–1514|date=2007|doi=10.1145/1240624.1240851|isbn=9781595935939|citeseerx=10.1.1.192.2364|s2cid=2011796}}</ref> both agree that the KLM model can be applied to predict task times on mobile devices, Li suggests further modifications to the model, by introducing a new concept called operator blocks. These are defined as "the sequence of operators that can be used with high repeatability by analyst of the extended KLM.”.<ref>{{cite book|last1=Li|first1=Hui|last2=Liu|first2=Ying|last3=Liu|first3=Jun|last4=Wang|first4=Xia|last5=Li|first5=Yujiang|last6=Rau|first6=Pei-Luen Patrick|title=Extended KLM for mobile phone interaction: a user study result|journal=CHI EA '10 CHI '10 Extended Abstracts on Human Factors in Computing Systems|date=2010|publisher=ACM|___location=New York|isbn=978-1-60558-930-5|page=3521}}</ref> He also discards old operators and defines 5 new mental operators and 9 new physical operators, while 4 of the physical operators focus on pen-based operations.
Rice and Lartigue <ref>{{cite book|last1=Rice|first1=A.D.|last2=Lartigue|first2=J. W.|title=Proceedings of the 2014 ACM Southeast Regional Conference |chapter=Touch-level model (TLM) |pages=1–6|date=2014|doi=10.1145/2638404.2638532|isbn=9781450329231|s2cid=25139034}}</ref> suggest numerous operators for touch devices together with updating existing operators naming the model TLM (Touch Level Model).
They retain the operators Keystroke (K/B), Homing (H), Mental (M) and Response Time (R(t)) and suggest new touch specific operators partly based on Holleis’ suggested operators:
* Distraction. A multiplicative operator that adds time to other operators.
* Pinch. A 2+ finger gesture commonly used to zoom out
* Zoom. A 2+ finger gesture commonly used to zoom in
* Initial Act. The action or actions necessary to prepare the system for use (e.g. unlocking device, tapping an icon, entering a password).
* Tap. Tapping some area of the screen to effect a change or initiate an action.
* Swipe. A 1+ finger gesture in which a finger or fingers are placed on the screen and subsequently moved in a single direction for a specified amount of time.
* Tilt. The tilting — or full rotation of — the entire device d degrees (or radians).
* Rotate. A 2+ finger gesture in which fingers are placed on the screen and then rotated d degrees (or radians) about a central axis.
* Drag. A 1+ finger gesture in which fingers are placed on the screen and then moved — usually in a straight line — to another ___location.
== See also ==
* [[Human-Computer Interaction]]
* [[Usability]]
* [[Usability Testing]]
* [[Human information processor model]]
* [[GOMS]]
* [[CMN-GOMS]]
* [[CPM-GOMS]]
==References==
{{reflist|2}}
==External links==
*Simple [http://courses.csail.mit.edu/6.831/2009/handouts/ac18-predictive-evaluation/klm.shtml KLM calculator] (free, web-based)
*Simple [http://www.syntagm.co.uk/design/klmcalc.shtml KLM calculator] (free, downloadable Windows app)
*The [http://klmformanalyzer.weebly.com/index.html KLM Form Analyzer (KLM-FA)], a program which automatically evaluates web form filling tasks (free, downloadable Windows app).
*The [
*[http://www.cs.umd.edu/class/fall2002/cmsc838s/tichi/goms.html GOMS by Lorin Hochstein]
[[Category:Human–computer interaction]]
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