`
`2012 Ninth International Conference on Information Technology- New Generations2012 Ninth International Conference on Information Technology - New Generations
`
`Usability Heuristics for Touchscreen-based
`Mobile Devices
`
`Rodolfo Inostroza1, Cristian Rusu1, Silvana Roncagliolo1, Cristhy Jiménez1,3, Virginica Rusu2
`
`1Pontificia Universidad Católica de Valparaíso, Valparaíso, Chile
`2Universidad de Playa Ancha, Valparaiso, Chile
`3Escuela Superior Politécnica de Chimborazo, Riobamba, Ecuador
`
`e-mails: info@randomstudio.com, cristian.rusu@ucv.cl, silvana@ucv.cl, cristhyjimenez@yahoo.es,
`virginica.rusu@upla.cl
`
`Abstract—Usability is a main quality attribute for any
`interactive product. Usability
`in touchscreen-based mobile
`devices is something essential and should be considered when
`launching a new product; it could be a distinguishing feature in a
`rushing market, as it is the one of the mobile devices nowadays.
`Traditional methods for usability measuring do not really fit the
`nature of these devices. There is a need for new usability
`evaluation methods or at least for the use of traditional
`evaluations in novel ways. A set of specific usability heuristics for
`touchscreen-based mobile devices is proposed and (preliminary)
`validated.
`
`Keywords—touchscreen-based mobile
`evaluation; usability heuristics.
`
`devices;
`
`usability
`
`INTRODUCTION
`I.
`is a mobile device which offers
`smartphone
`A
`functionalities beyond just a phone call. There are different
`kinds of smartphones, where touchscreen-based devices stand
`out among others, being the most popular nowadays.
`The ISO/IEC 9241 standard defines the usability as the
`extent to which a product can be used by specified users to
`achieve specified goals with effectiveness, efficiency and
`satisfaction, in a specified context of use [1]. Usability
`evaluation of a product is one of the most important stages in
`the user centered design approach. It allows obtaining the
`usability characteristics of a product, in this case touchscreen-
`based mobile devices, and the extent to which the usability
`attributes, usability paradigms and usability principles are
`being accomplished.
`Usability evaluation methods are commonly divided into
`inspection and testing methods. Inspection methods find
`usability problems based on
`the expertise of usability
`professionals. Testing methods find usability problems through
`the observation of the users while they use (and comment on) a
`system interface [2].
`Heuristic evaluation is a widely used inspection method [3]
`[4]. They are easy to perform, cheap and able to find many
`usability problems (both major and minor problems). However,
`
`it may miss domain specific problems. That is why the use of
`appropriate heuristics is highly significant.
`Usability evaluation for applications based on emerging
`information technology brings new challenges. Is it the
`classical concept of usability still valid? Which are the
`dimensions of the (new) usability? How can it be measured?
`How should we develop for (better) usability? There is a need
`for new evaluation methods or at least for the use of traditional
`evaluations in novel ways [5].
`Traditional usability evaluation methods do not consider the
`particularities of the touchscreen-based mobile devices and the
`physical user interface. This leads to a need of new techniques
`for an accurate usability evaluation for touchscreen-based
`mobile devices.
`The present work focuses on usability evaluation of
`touchscreen-based mobile devices, by heuristic evaluations. A
`set of 11 specific usability heuristics is proposed and
`(preliminary) validated. Section II highlights
`the main
`characteristics of touchscreen-based mobile devices, such as
`taxonomy, physical user interface components and challenges
`of usability evaluation in these devices. Section III presents the
`methodology that has been used in heuristics’ development and
`a description of the iterations that have been done up to date.
`The touchscreen-based mobile devices usability heuristics
`proposal is presented in Section IV. Section V shows the
`proposal’s preliminary validation. Section VI presents the
`preliminary conclusions and future works.
`
`II.
`
`CHALLENGES OF USABILITY EVALUATION IN
`TOUCHSCREEN-BASED MOBILE DEVICES
`A mobile device can be defined as a small gadget with
`some basic processing capabilities, with permanent or
`intermittent wireless network connection and limited memory
`capacity. A mobile device has usually been designed for a
`specific function, but it can also perform additional general
`tasks.
`and
`communication
`are portable
`Mobile devices
`information systems, characterized by three key aspects which
`
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`978-0-7695-4654-4/12 $26.00 © 2012 IEEE978-0-7695-4654-4/12 $26.00 © 2012 IEEE
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`DOI 10.1109/ITNG.2012.134DOI 10.1109/ITNG.2012.134
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`affect their user interface design: (1) they are mainly used in
`the user’s hands, (2) they are used wirelessly and (3) they
`support
`the addition of new applications and
`internet
`connection [6]. Other important aspects to consider when
`evaluating the usability of mobile devices are: (1) they have
`small screen size even if they have to display large amounts of
`information, (2) the buttons of the device generally have more
`than one function, and (3) the devices have limited processing
`and memory capabilities [7].
`Schiefer and Decker (2008) classify the mobile devices by
`size and weight, data input/output modes, performance, kind of
`usage, communication capabilities, type of operating system
`and expandability [8]. The mobile devices may be classified as
`follows: (1) mobile standard PC, (2) mobile internet devices,
`(3) handhelds or PDAs, (4) smartphones, (5) feature phones,
`(6) simple phones and (7) special terminals.
` Touchscreen-based mobile devices belong to categories
`(1), (2), (3) and (4). This research focuses mainly on touch
`phones [9]. However, the results can be adapted to other
`touchscreen-based mobile devices.
`The unique features and characteristics of touchscreen-
`based mobile devices that make the usability evaluation a
`challenging process may be defined as follows [10]:
`• Mobile context of use: All aspects related to the
`interaction between the user, the system and the
`environment occur concurrently. Auditive distraction
`(e.g.: noise) or visual distraction (e.g.: excess or lack of
`lighting), can disturb the user. A proper evaluation
`method should consider most of the context of use
`characteristics.
`Small screen size: To make information fit in a small
`display can be not aesthetically pleasing, or even worst,
`completely
`illegible. Different
`tests
`should be
`performed, considering distinct screen sizes.
`Screen resolution: Low screen resolution can degrade
`the perceived quality of the multimedia data displayed
`in the device screen. Different screen resolutions may
`lead to significantly different usability issues.
`Limited processing, memory and energy capabilities:
`Some applications require large amounts of memory
`and/or processing power for graphical support and data
`processing, which can exceed the device capabilities.
`The system performance may vary according to
`available memory, energy and processing power.
`These
`issues should be considered
`in usability
`evaluations.
`• Data entry methods: Small buttons and labels can
`reduce the efficiency and effectivity in data entry,
`reducing the data entry speed and raising the error rate.
`Evaluations that minimize the impact of data entry
`methods should be performed (as long as they are not
`the research focus).
`
`•
`
`•
`
`•
`
`•
`
`•
`
`•
`
`•
`
`III. DEFINING TOUCHSCREEN-BASED MOBILE DEVICES
`USABILITY HEURISTICS
`Usability inspections, including heuristic evaluation, are
`well documented and many publications describe the usage of
`these methods. Literature usually focuses on describing the
`advantages and disadvantages of usability evaluation methods
`but not on how to develop new methods and/or usability
`heuristics.
`In order to develop specific usability heuristics for
`touchscreen-based mobile devices, 6 steps methodology was
`followed [11]:
`•
`STEP 1: An exploratory stage, to collect bibliography
`related to touchscreen-based mobile devices, their
`characteristics, general and/or related (if there are
`some) usability heuristics.
`STEP 2: A descriptive stage, to highlight the most
`important characteristics of the previously collected
`information, in order to formalize the main concepts
`associated with the research.
`STEP 3: A correlational stage,
`the
`identify
`to
`characteristics that usability heuristics for touchscreen-
`based mobile devices should have, based on traditional
`heuristics and case studies analysis.
`STEP 4: An explicative stage, to formally specify the
`set of touchscreen-based mobile devices heuristics,
`using a standard template.
`STEP 5: A validation (experimental) stage, to check
`touchscreen-based mobile devices heuristics against
`traditional (Nielsen’s) heuristics by experiments,
`through heuristic evaluations performed on selected
`case studies, complemented by user tests.
`STEP 6: A refinement stage, based on the feedback
`from the validation stage.
`STEP 1 explored specific
`touchscreen-based mobile
`devices characteristics,
`taxonomy and usability-related
`aspects.
`STEP 2 re-examined the meaning of usability and its
`characteristics, in the context of touchscreen-based mobile
`devices.
`As no specific and/or related touchscreen-based mobile
`devices usability heuristics were found, Nielsen’s 10 well
`known and extensively used heuristics were used at STEP 3
`[4].
`The standard template used at STEP 4 was the following
`one:
`•
`
`•
`
`•
`
`•
`
`663663
`
`ID, Name and Definition: Heuristic’s identifier, name
`and definition.
`Explanation: Heuristic’s
`explanation,
`detailed
`including references to usability principles, typical
`usability problems, and related usability heuristics
`proposed by other authors.
`Examples: Examples of heuristic’s violation and
`compliance.
`
`2
`
`

`

`•
`
`•
`
`Benefits: Expected usability benefits, when
`heuristic is accomplished.
`Problems: Anticipated
`misunderstanding, when
`evaluations.
`
`of
`problems
`performing
`
`A. First Iteration
`In a first iteration, STEPS 1, 2 and 3 of the above described
`methodology were followed. At STEP 1, a critical review of
`related literature was performed.
`At STEP 2, main concepts regarding touchscreen-based
`mobile devices were formalized, such as taxonomy, physical
`user interface characteristics and ergonomics, among others.
`At STEP 3, a guided inspection was carried out using
`Nielsen’s heuristics, in order to identify usability issues and
`positive characteristics of the analyzed devices. A first set of
`usability heuristics for touchscreen-based mobile devices was
`developed, without using a formal specification template. The
`initial proposal consisted of 11 usability heuristics:
`•
`10 heuristics were inspired by Nielsen’s heuristics and
`complimented by the formalized concepts regarding
`touchscreen-based mobile devices (defined at STEP 2).
`• Heuristic no. 11 was obtained through the analysis of
`mobile concepts, positive aspects and usability issues.
`The usability heuristics set was complimented by a basic
`checklist proposal.
`
`B.
`
`Second Iteration
`The set of usability heuristics obtained after performing the
`first iteration was refined through the execution of a second
`iteration. STEPS 5, 6, and 4 were carried out, in this order.
`At STEP 5, as an adapted validation stage, the usability
`heuristics set was critically reviewed by a usability expert.
`At STEP 6, some of the usability heuristics were redefined
`according to the feedback received at STEP 5.
`STEP 4 led to a formally specified set of usability heuristics
`for touchscreen-based mobile devices, using the standard
`template defined above.
`
`C.
`
`Third Iteration
`After the second iteration, a new validation and refinement
`process was carried out. STEPS 5, 6 were followed, in this
`order.
`At STEP 5, a guided inspection was performed. The
`evaluation was carried out on a Blackberry Storm device, by 4
`evaluators, grouped by the level of expertise. The two most
`experienced evaluators used Nielsen’s heuristics; the two less
`experienced evaluators used the touchscreen-based mobile
`devices heuristics proposal.
`Data obtained at STEP 5 was analyzed at STEP 6, in order
`to build a list of observations and possible improvements to the
`proposal. A mapping between the touchscreen-based mobile
`
`the
`
`devices heuristics proposal and Nielsen’s heuristics was built,
`in order to highlight similarities and differences.
`
`heuristic
`heuristic
`
`IV. A SET OF USABILITY HEURISTICS FOR TOUCHSCREEN-
`BASED MOBILE DEVICES
` The usability heuristics proposal for touchscreen-based
`mobile devices is presented below.
`(TMD1) Visibility of system status: The device should keep
`the user informed about all the processes and state changes
`through the use of a specific kind of feedback, in a reasonable
`time.
`(TMD2) Match between system and the real world: The
`device should speak the users' language with words, phrases
`and concepts familiar to the user, instead of system-oriented
`concepts and/or technicalities. The device should follow the
`real world conventions and physical laws, displaying the
`information in a logical and natural order.
`(TMD3) User control and freedom: The device should
`allow the user to undo and redo his actions, and it should
`provide "emergency exits” to leave the unwanted state. These
`options should be clearly pointed, preferably through a physical
`button or similar; the user shouldn’t be forced to pass through
`an extended dialogue.
`(TMD4) Consistency and standards: The device should
`follow the established conventions, on condition that the user
`should be able to do things in a familiar, standard and
`consistent way.
`(TMD5) Error prevention: The device should have a careful
`graphic user interface and physical user interface design, in
`order to prevent errors. The non-available functionalities
`should be hidden or disabled and the user should be able to get
`additional information about all available functionality. Users
`should be warned when errors are likely to occur.
`(TMD6) Minimize the user's memory load: The device
`should minimize the user's memory load by making objects,
`actions, and options visible. The user should not have to
`remember information from one part of the dialogue to another.
`Instructions for use of the system should be visible or easily
`retrievable whenever appropriate.
`(TMD7) Customization and shortcuts: The device should
`provide basic configuration options and should give expert
`users access to advanced configuration options. The device
`should provide shortcuts to the most frequent tasks and should
`allow their customization and/or definition.
`(TMD8) Aesthetic and minimalist design: The device
`should avoid displaying
`irrelevant or
`rarely needed
`information. Each extra information unit reduces the system
`performance.
`(TMD9) Help users recognize, diagnose, and recover from
`errors: Error messages in the device should be expressed in
`plain language (no codes), precisely indicating the problem,
`and constructively suggesting a solution.
`(TMD10) Help and documentation: The device should
`provide easy-to-find documentation and help, centered on the
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`user’s current task. A list of concrete (and not too large) steps
`to carry out should be provided.
` (TMD11) Physical interaction and ergonomics: The device
`should provide physical buttons or similar user interface
`elements for main functionalities. Elements should be placed in
`a recognizable position. The device dimensions, shape, and
`user interface elements in general, should fit the natural posture
`of the hand.
`The full specification of heuristic TMD1 is shown below.
`•
`ID: TMD1
`•
`Name: Visibility of system status
`• Description: The device should keep the user informed
`about all the processes and state changes through the
`use of a specific kind of feedback, in a reasonable time.
`Explanation: Through the interaction with the device,
`the user can perform many tasks. These actions can
`lead to changes in the system status, which should be
`informed to the user, one way or another. Changes that
`occur without the intervention of the user, but require
`the user interaction (e.g.: incoming phone calls, video
`calls, email messages, timer alert, low battery alert)
`should also be informed.
`The specific feedback methods may use:
`Sound (e.g.: ringtone, message tone, email tone,
`o
`low battery tone, camera shutter sound). These
`sounds should be distinctive (by default) and
`customizable.
`Lights (e.g.: notification light, under button light,
`camera flash).
`o Graphic information (e.g.: static icon, animated
`icon, text notification, pop-up alert message, pop-
`up error message).
`o Vibration.
`•
`Examples:
`Fig. 1 shows some examples of specific feedback on a
`Nokia X6 touch phone. Graphic information feedback can be
`seen on the left side of the image: (a) pop-up alert message,
`indicating the existence of a new instant messaging message;
`(b) static icon, indicating the same information. An example of
`notification light is displayed on the right side of the image.
`•
`Benefits:
`Improved experience of use: Specific feedback helps
`user to properly react to events, improving her/his
`experience.
`Better system status control: Specific feedback helps
`user to be aware if there are changes in the system
`status.
`Problems: It could be difficult to distinguish between
`the lack of feedback and the delayed feedback, due to
`performance issues. When using the device, the
`available memory, battery charge level and running
`
`•
`
`•
`
`o
`
`applications affect the device performance, which can
`delay or even disable some types of feedback.
`
`Figure 1. Examples of specific feedback on Nokia X6 device.
`Table 1 presents the mapping between the 11 usability
`heuristics for touchscreen-based mobile devices and Nielsen’s
`10 heuristics.
`
`TABLE I.
`
`MAPPING BETWEEN TOUCHSCREEN-BASED MOBILE DEVICES
`HEURISTICS AND NIELSEN'S HEURISTICS
`
`Touchscreen-based mobile devices
`heuristics
`Name
`Visibility of system
`status
`Match between system
`and the real world
`User control and
`freedom
`Consistency and
`standards
`Error prevention
`Minimize the user's
`memory load
`Customization and
`shortcuts
`Aesthetic and minimalist
`design
`Help users recognize,
`diagnose, and recover
`from errors
`Help and documentation H10
`Physical interaction and
`ergonomics
`
`Id
`TMD1
`
`TMD2
`
`TMD3
`
`TMD4
`TMD5
`TMD6
`
`TMD7
`
`TMD8
`
`TMD9
`
`TMD10
`TMD11
`
`Id
`H1
`
`H2
`
`H3
`
`H4
`H5
`H6
`
`H7
`
`H8
`
`H9
`
`Nielsen’s heuristics
`Name
`Visibility of system status
`Match between system and
`the real world
`User control and freedom
`
`Consistency and standards
`Error prevention
`Minimize the user's
`memory load
`Flexibility and efficiency
`of use
`Aesthetic and minimalist
`design
`Help users recognize,
`diagnose, and recover from
`errors
`Help and documentation
`
`Touchscreen-based mobile devices usability heuristics
`TMD1 to TMD10 particularize Nielsen’s heuristics H1 to H10,
`based on the touchscreen-based mobile devices characteristics.
`Although heuristics names are quite similar, their definitions
`are substantially different. For instance, the touchscreen-based
`mobile devices heuristic (TMD5) and the related Nielsen’s
`heuristic (H5) have the same name (“Error prevention”), but
`the heuristics’ meanings are radically different, as table 2
`shows.
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`TABLE II.
`
`COMPARISON BETWEEN HEURISTICS TMD5 AND H5, “ERROR
`PREVENTION”.
`
`TABLE III.
`
`USABILITY PROBLEMS IDENTIFIED IN BLACKBERRY STORM2.
`
`Group 2: Using Nielsen’s
`heuristics
`Number
`of
`problems
`2
`4
`1
`4
`3
`1
`5
`3
`0
`0
`
`Average
`Severity
`
`3.25
`1.80
`4.00
`2.50
`3.00
`2.50
`3.40
`2.83
`0
`0
`
`Id
`
`H1
`H2
`H3
`H4
`H5
`H6
`H7
`H8
`H9
`H10
`
`23
`Total
`Average Severity
`
`2.33
`
`Group 1: Using touchscreen-based
`mobile devices heuristics
`Id
`Number
`Average
`of
`Severity
`problems
`3
`TMD1
`9
`TMD2
`2
`TMD3
`2
`TMD4
`2
`TMD5
`1
`TMD6
`5
`TMD7
`2
`TMD8
`1
`TMD9
`1
`TMD10
`2
`TMD11
`30
`Total
`Average Severity
`
`3.17
`2.83
`2.75
`3.50
`3.50
`2.50
`2.80
`4.00
`4.00
`3.00
`3.00
`
`3.19
`
`TMD5 – Error prevention
`The device should have a careful
`graphic user interface and physical
`user interface design, in order to
`prevent errors. The non-available
`functionalities should be hidden or
`disabled and the user should be able
`to get additional information about
`all available
`functionality. Users
`should be warned when errors are
`likely to occur.
`
`H1 – Error prevention
`Even better than good error messages
`is a careful design which prevents a
`problem from occurring in the first
`place. Either eliminate error-prone
`conditions or check for them and
`present users with a confirmation
`option before they commit to the
`action.
`
`V.
`
`USABILITY HEURISTICS FOR TOUCHSCREEN-BASED
`MOBILE DEVICES IN PRACTICE: EARLY
`VALIDATION
` As described in Section III.C, a guided inspection was
`performed as an early validation experiment. The set of 11
`touchscreen-based mobile devices heuristics were evaluated
`against Nielsen’s heuristics, in one case study. The evaluation
`was performed on a Blackberry Storm 2 (9550) device/
`Blackberry Operating System (v. 5.0.0.1015). The following
`applications were analyzed: (1) menu, (2) name and address
`book, (3) calendar, (4) messaging and (5) camera.
`The inspection was carried out by two separate groups of
`evaluators, in equal conditions. Each group was composed by
`two evaluators, of similar level of expertise. One group used
`only the set of touchscreen-based mobile devices heuristics,
`while the other group used only Nielsen’s heuristics. Usability
`problems found by the two groups were then compared.
`A total of 53 usability problems were identified by the four
`evaluators. More usability problems were captured using the
`touchscreen-based mobile devices heuristics,
`than using
`Nielsen’s heuristics:
`•
`(P1) 18 usability problems (34%) were identified by
`both groups of evaluators,
`(P2) 21 usability problems (40%) were identified only
`by the group that used the touchscreen-based mobile
`devices heuristics,
`(P3) 14 usability problems (26%) were identified only
`by the group that used Nielsen’s heuristics.
`Table III shows the number of usability problems identified
`by each group of evaluators, grouped by heuristics. It also
`shows the average severity of the usability problems (on a 0 to
`4 severity scale).
`Evaluators that used touchscreen-based mobile devices
`heuristics were able to identify more usability problems than
`the evaluators that used Nielsen’s heuristics, even if their level
`of expertise was slightly lower. Moreover, the usability
`problems identified by the first group of evaluators were
`qualified as more sever (an average severity of 3.19, while the
`second group scored an average severity of 2.33). In a rough
`evaluation, it seems that the set of 11 touchscreen-based mobile
`devices heuristics works better than Nielsen’s heuristics.
`
`•
`
`•
`
`The possible correlation between the two series presented
`in table III was examined. As TMD11 has no equivalent in the
`Nielsen’s heuristics set, the value associated to TMD11 was
`eliminated. The correlation coefficient is 0.647; therefore the
`relationship may be described as moderate.
`The average number of usability problems per heuristic was
`2.8, when applying
`touchscreen–based mobile devices
`heuristics, respectively 2.3, when applying Nielsen’s heuristics.
`In order to check if the difference is significant, the T test was
`applied. Variances are not significantly different, as the F test
`showed. Consequentially, the T test for equal variances was
`applied.
`The T value was 1.73, and its associated probability was 0.3
`(being the level of significance 0.05). Therefore the 0.5
`difference between the average numbers of problems will not
`be considered as significant.
`In other words, both evaluation tools (touchscreen–based
`mobile devices heuristics and Nielsen’s heuristics) identify
`usability problems in similar way. Nevertheless, the proposed
`set of 11 heuristics seems to be more appropriate, as it was able
`to identify (slightly) more usability problems than the Nielsen’s
`set of heuristics. This is just a preliminary and quite early
`conclusion, and more experiments have to be done.
`Question arises with problems (P3). Why these problems
`were not identified when using the touchscreen-based mobile
`devices heuristics?
`The 14 usability problems identified only by the group that
`used Nielsen’s heuristics were associated to heuristics H7 –
`Flexibility and efficiency of use (5 problems), H4 – Consistency
`and standards (4 problems), H2 – Match between system and
`the real world (4 problems), H8 – Aesthetic and minimalist
`design (3 problems), H5 – Error prevention (3 problems), H1 –
`Visibility of system status (2 problems), H6 – Minimize the
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`ACKNOWLEDGMENT
`The authors would like to thank to all the participants
`involved into the experiments that the present study required.
`The work was highly supported by the School of Informatics
`Engineering of the Pontifical Catholic University of Valparaiso
`– Chile and by the Polytechnic School of Chimborazo –
`Ecuador.
`
`[3]
`
`[4]
`
`[6]
`
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`[9]
`
`user's memory load (1 problem) and H3 – User control and
`freedom (1 problem). The set of the touchscreen-based mobile
`devices heuristics provides similar tools that can potentially
`identify all these problems (heuristics TMD7, TMD4, TMD2,
`TMD8, TMD5, TMD1, TMD6 and TMD3, respectively).
`Therefore, it seems that evaluators that used the touchscreen-
`based mobile devices heuristics subjectively ignored problems
`(P3).
`Table IV shows the average severity of the problems
`detected by group using each set of heuristics and the number
`and severity average of problems detected by both. The
`average severity of problems (P3) is the lowest one. Again, it
`seems that the touchscreen-based mobile devices heuristics
`worked better than Nielsen’s heuristics.
`
`SEVERITY AVERAGE BY GROUP
`TABLE IV.
`Problems identified
`Number of
`problems
`
`By both groups of evaluators
`Using touchscreen-based
`mobile devices heuristics
`Using Nielsen’s heuristics
`
`18
`21
`14
`
`Average
`Severity
`3,14
`3,00
`2,68
`
`Id
`
`P1
`P2
`P3
`
`VI. CONCLUSIONS
`Usability in touchscreen-based mobile devices is something
`essential and should be considered when launching a new
`product, as it could be a distinguishing feature in a rushing
`market as the one of mobile devices nowadays. There is a need
`for new usability evaluation methods or at least usability
`evaluations should be particularized for touchscreen-based
`mobile devices.
`A set of 11 specific usability heuristics was developed. Early
`validation proved its usefulness and potential. However, more
`experiments are necessary.
`A right balance between specificity and generality should be
`followed. If heuristics are too specific, they will probably
`become hard to understand and hard to apply. General
`heuristics, complemented by specific usability checklists, will
`probably work better, most of the time.
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