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Evaluation of User Interfaces for Displaying Text Messages on Mobile Devices

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More and more information such as short text messages (SMS) or emails is stored on mobile phones. Retrieving the right information at the right time has become a diffi-cult task when using traditional interfaces included in to-day's cell phones. We created two novel user interfaces (one textual and one graphical) and compared both to the classical interface for retrieving stored SMS messages in a 34-participant usability experiment. Both novel interfaces yielded significantly better results than the existing classi-cal interface. Moreover, the results show that the novel tex-tual interface, which groups messages by social contacts, outperforms the complex graphical interface, which dis-plays messages in a chessboard-like grid. Both objective and subjective findings are in favor of the textual interface except for one result: The graphical interface is more en-joyable than the textual one.
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EVALUATION OF USER INTERFACES FOR DISPLAYING TEXT MESSAGES
ON MOBILE DEVICES
Olaf Thiele
University of Mannheim, Germany
Email: thiele@uni-mannheim.de
Pascal S¨utterlin
University of Mannheim, Germany
Email: suetterlin@bwl.uni-mannheim.de
Lars Kaczmirek
Centre for Survey Research and Methodology, Germany
Email: kaczmirek@zuma-mannheim.de
ABSTRACT
More and more information such as short text messages
(SMS) or emails is stored on mobile phones. Retrieving
the right information at the right time has become a diffi-
cult task when using traditional interfaces included in to-
day’s cell phones. We created two novel user interfaces
(one textual and one graphical) and compared both to the
classical interface for retrieving stored SMS messages in a
34-participant usability experiment. Both novel interfaces
yielded significantly better results than the existing classi-
cal interface. Moreover, the results show that the novel tex-
tual interface, which groups messages by social contacts,
outperforms the complex graphical interface, which dis-
plays messages in a chessboard-like grid. Both objective
and subjective findings are in favor of the textual interface
except for one result: The graphical interface is more en-
joyable than the textual one.
KEY WORDS
Mobile Computing Contexts, User Interfaces, Information
Visualization, Evaluation
1 Introduction
The information stored on mobile phones has increased im-
mensely in recent years. While in the 1990s mobile phones
were mainly used for making phone calls, they have be-
come the digital companion affordable to almost everyone
in today’s world. Most modern phones include a camera,
can play charts as ring tones and have processor perfor-
mance which is equal to basic game consoles. While new
functionalities and memory capacity are constantly added,
few considerations are made concerning the management
of the large amount of data. For example, SMS message
boxes with 300 stored messages have the same retrieval in-
terface as ten-year old cell phones holding a maximum of
10 messages. While this was a technical necessity in the
past, new programming packages introduce the possibility
to create novel user interfaces for retrieving stored SMS
messages.
Nevertheless, what should a new interface for mobile
devices look like? Both technical possibilities and human
preferences have to be taken into account. To find out more
about an optimal design, we created two new interfaces
for accessing stored SMS messages and evaluated them.
The first novel interface is the list interface, which is sim-
ilar to the classical interface in use today, except for two
differences. Incoming and outgoing messages are joined
and subsequently ordered by communication partner. Af-
ter clicking on a communication partner, the user sees a list
of all inbound and outbound messages sorted by date. In
other words, the list shows both sides of a “conversation”
in the sequence in which it occurred as opposed to the clas-
sical interface, which shows individual transmissions one
at a time. While the list interface looks similar to the clas-
sical one, we designed the other novel interface to be more
complex. The graphical interface allows for sophisticated
usage. It places all messages in a chessboard-like grid and
thus offers a good overview of conversations with one or
more partners over time. However, due to its high level
of abstraction, the model behind it needs to be learned and
internalized. Finally, we created a classical interface as a
baseline for the experiment.
We evaluated the two novel interfaces and the clas-
sical one in a usability study. Test persons received mo-
bile phones and could use them freely, but all worked on
the same message basis for each of the six given scenar-
ios. All events, such as message opening and closing times,
or time spans between events, where logged for objective
evaluation. Results show that the list interface concerned
with objective and subjective usability as well as retrieval
success outperforms the graphical interface. Our consid-
erations and findings are laid out in detail in the sections
below. The first section deals with background informa-
tion on SMS communication, the second section describes
the technical progress, and related work is discussed in the
following section. Both novel user interfaces are presented
thoroughly in section three, including design decisions and
technical realization. Section four introduces the method-
ology of the experiment, followed by its results in section
five. The implications are discussed in the subsequent sec-
tion. The last section concludes with final thoughts based
on our findings regarding real world adoption of mobile in-
formation retrieval interfaces.
2 Background
2.1 SMS retrieval problems
SMS messages are the predominant means of textual com-
munication when using mobile phones. According to the
Netsize Guide 2005, SMS volume increased from 16 bil-
lion messages in 2001 to 36 billion in 2003 in Germany
alone [1, p.131]. The Guide states that today over 200 bil-
lion SMS messages are exchanged in Europe per month.
These account for 70% of data communication over mobile
networks [1, p.32]. However, the basic principle for ac-
cessing stored messages on mobile phones has not changed
at all. First, incoming and outgoing messages are stored
in two distinct lists. Second, the lists are sorted by date,
i.e. when the message was sent or received, in descending
chronological order. This retrieving principle has been a
feasible solution for a long time. Explaining how messages
are stored takes only seconds due to the simplicity of the
concept. Furthermore, accessing messages on a different
phone is in most cases very easy. We programmed our own
classical baseline SMS interface for the study and were sur-
prised how fast test persons learned to use it. This classical
technique works well with small numbers of messages. If
only 20 or 30 messages need to be screened, the interface
works well. Problems arise, however, when larger numbers
of messages need to be stored. SMS storage capacities of
200 or more are common today and are likely to increase
in the future.
2.2 Technological foundation
Early models of mobile phones could only be used to make
phone calls and send SMS messages. Today’s phones have
enough processing power to encrypt phone calls in real
time without using special hardware. This development of-
fers the possibility to program complex applications like
the graphical interface used in this study.
The Java 2 Micro Edition (J2ME) from Sun is the
predominant programming model for mobile phones at the
moment [2]. It is used to build small programs called MI-
Dlets. A MIDlet can be seen as a classic Java applet that
is loaded onto a mobile phone. MIDlets use a subset of
the Java language and offer a wide range of functionality.
We used the MIDlets to create all three SMS interfaces em-
ployed in our study.
2.3 Related Work
We found the following three fields of research to be inter-
related with our study: information retrieval interfaces for
mobile devices, general visual information retrieval and vi-
sualizations for the semantic web. Only few evaluations
of graphical information retrieval interfaces for mobile de-
vices have been published. Marcus complains about the
lack of research in this area: “One aspect that has received
relatively little attention is information visualization” [3,
sec.5]. One of the few studies was carried out by Masood-
ian and Lane who evaluated travel itinerary visualizations
[4]. They compared a textual travel itinerary application
with a visual one based on the Wireless Application Proto-
col (WAP). Masoodian and Lane conclude that the textual
representation was more effective than the visual one due
to the laboratory setting [4, sec. 6].
The field of general visual information retrieval has
received more attention from researchers. Hearst gives
an extensive overview of available techniques in 1999 [5,
chap. 10]. In recent years, Donath developed the “Loom
Project” which shows graphical illustration of Usenet con-
versations [6, p. 48]. Conversations are drawn as circles,
with e-mails building the arch. The more e-mails a conver-
sation comprises, the bigger the circle. Furthermore, col-
ors are used to differentiate between different speakers in a
conversation.
The field of semantic web visualization gives even
more suggestions on how semantic information might be
appropriately visualized. Fluit, Sabou and van Harme-
len use given ontologies to draw interrelations between re-
sources [7]. Again, dimensions like size, shape, position or
color are employed to represent abstract relationships be-
tween entities. A good overview of other visual interface
approaches for semantic information retrieval is given by
B¨orner [8].
3 SMS retrieval interfaces
Three different interfaces were applied in the study: the
classic interface representing the predominant user inter-
face found in most modern mobile phones today, the list
interface with a moderate level of abstraction showing mes-
sages ordered by communication partner and finally a com-
plex visual interface with a chessboard-like structure. The
two novel interfaces were derived from research on exist-
ing interfaces and SMS messaging usage. While related
work has been presented in Subsection 2.3, the main func-
tions and contexts of SMS messaging are presented in the
following subsection. Subsequently, the two novel inter-
faces and the classical interface are presented together with
design descriptions and alternatives.
3.1 Functions and contexts of SMS usage
In order to find a new user interface for SMS messages,
one needs to take the main functions of SMS usage into ac-
count. oring’s reports five functions of SMS messages:
contact, information, appeal, obligation and declaration [9,
p. 27], with contact and information being the most fre-
quent functions (combined usage 88%).
In a study of mobile phone usage among teenagers,
Pedersen found that most users currently send ordinary
SMS messages instead of multimedia messages or other
SMS-based commercial services [10, p. 66]. He also
Figure 1. Screenshots list user interface
states that applications or services for sharing messages
with friends or organizing important messages is still miss-
ing [10, p. 67].
In a recent study Tamminen et al. state that the context
of mobile phone usage should be considered when design-
ing a user interface [11]. They point out that mobile appli-
cations should be especially aware of the social contacts of
the user [11, p. 141]. Rodden et al. support this view in
their work on design for mobile contexts [12]. They argue
that a successful novel software design needs to combine
the contexts of both the virtual and real world.
3.2 The classical interface
In order to have the same look and feel for all three in-
terfaces, we rebuilt a standard SMS interface as the base-
line for the novel ones. Other advantages of programming
our own classical interface are the possibility to record user
behavior through the application and using the same mes-
sages for all three interfaces.
3.3 The list interface
The list interface is the first novel interface and was de-
signed to give a comprehensive overview of the underlying
message base. In contrast to the classical interface, both
incoming and outgoing messages are combined and then
sorted by communication partner for the list interface. The
starting screen of the application shows an alphabetical list
of communication partners. If one of them is selected by
clicking on the name, a list of messages sorted chronologi-
cally is displayed. Each line represents one message and is
comprised of an icon showing the direction of communica-
tion, together with the date and time the message was sent.
Figure 1 shows two screenshots: the list of all communi-
cation partners and list of messages from and to a single
communication partner.
The list interface was designed to ease navigation. As
described in Section 3.1, Tamminen et al. ask for applica-
tions to take the social contacts of the user into account [11,
p. 141]. By organizing the list interface around social con-
tacts, queries where the communication partner is obvious
but the exact time frame unknown are solved easily (e.g.
“He sent me his address, but I can’t remember when.”).
Furthermore, conversations are much easier to comprehend
because no interfering messages are displayed.
Figure 2. Basic principle and screenshot of the visual inter-
face
3.4 The visual interface
The design rationale for the second novel interface - the
visual interface - was to build a graphical information re-
trieval application that facilitates the comprehension of
conversations as well as showing interrelations of messages
over time.
The visual interface is composed of a chessboard-like
grid where messages are represented by a circle. For this
study, the grid was comprised of (18x18) 324 fields, each
field containing only one or no message. Each row of
the grid represents one day, the top row is the present day
and the bottom row is 18 days before that. Columns were
grouped into three categories: the leftmost columns repre-
sent the morning of a day, the middle columns show after-
noon messages and columns on the right display evening
messages. The ten most frequent communication partners
have a distinct color, all others are black. Incoming mes-
sages are depicted by a shaded circle, while outgoing mes-
sages are indicated by an empty circle (analogous to the
list interface). Figure 2 depicts the basic principle and a
screenshot of the graphical interface.
The grid is split into 9 screens because not all 324
fields of the model can be drawn together on the display
of a mobile device. Each screen contains (6x6) 36 fields.
Users navigate through the screens by using a small joy-
stick found on most modern mobile phones, moving one
field at a time and allowing movements into the four main
directions: up, down, left and right. Clicking on one of the
circles opens the corresponding message.
To facilitate navigation between grids, small arrows
at the four sides indicate whether there is another screen
in that direction or not. The cursor is depicted by a small
square. If the cursor is placed on a position holding an
SMS, the date and time, communication partner and direc-
tion of communication (incoming or outgoing) is shown in
the bars at the top and bottom. If the cursor is placed on an
empty position, date and timeframe (morning, afternoon or
evening) are displayed. The application always starts in the
upper left screen (morning of present day).
4 Experimental evaluation
4.1 Hypotheses
We conducted an experiment to explore the usability dif-
ferences between the classical, list and graphical interface.
Following our lines of thought in designing the novel inter-
faces we formulated two hypotheses:
H1: Both novel interfaces are equal or better than the
existing classical interface because of enhanced func-
tionality and better data representation.
H2: The list interface is superior to the graphical in-
terface due to its reduced complexity and its focus on
social relations.
4.2 Design and procedure
The experiment was comprised of six different scenarios
that were grouped into two task types: group contact and
single contact. For the first task group contact, scenar-
ios were constructed as a conversation happening within
a short period of time (e.g. one afternoon) with two com-
munication partners. Scenarios for the second task (single
contact) consisted of comprehending a conversation over a
long period of time with only a single communication part-
ner. Messages were scattered over the whole 18 day time
period (e.g. finding a birthday present for a friend). To
be able to show that differences in the measures are due
to the experimental design it is important to control other
sources who could have an impact on the dependant vari-
ables. Therefore, all participants worked on the same text
message base.
For training purposes, participants were asked to
solve the first scenario with the classical interface. Scenar-
ios 2-5 were solved using the list interface and the graphi-
cal one respectively. Scenario 6 served as the baseline with
participants using the classical interface for solving a more
simple problem. Each scenario was built in the following
way: participants received contextual and chronological in-
formation. Afterwards, they were asked to solve two prob-
lems related to the scenario. Finally, test persons answered
a questionnaire after completing each scenario. As for ma-
terials, two Nokia 6230 mobile phones were used for the
study. As for time, most experimental sessions lasted about
40 minutes.
4.3 Measures
Time to complete a given task and retrieval success were
used as objective measures, while a questionnaire served
as a subjective measure in the experiment. The data col-
lected from the phones following the experiments was the
main data base for the objective assessment. We stored the
following four user events in the log file of the applica-
tion: beginning and end of the scenario, opening and clos-
ing times of a message. The retrieval success data was
derived from automatically counting how many messages
were opened in total and how many of those were related
to the given task. After they had performed the respec-
tive scenario, participants were asked to complete a ques-
tionnaire containing five items typically used in usability
testing: perceived ease of use, perceived usefulness, enjoy-
ment, attitude toward behavior and intention to use. The
items draw on the work of Venkatesh, Morris and Davis
and incorporate the Technology Acceptance Model which
is supplemented by intrinsic motivation [13, p. 428]. The
answer categories consisted of a 7-point-scale with labels
at both endings. Participants had to rate in how far they felt
given statements in the questionnaire are applicable to the
interface at hand.
4.4 Sample
The sample is comprised of 34 first year university students
who participated in early 2005 in the experiment. The ma-
jority of test persons report sending SMS messages on a
daily basis or at least once a week (82%). They receive
a median of 66 text messages per month, and they report
sending the same number of messages to other contacts. A
quarter of the participants reopen messages stored on their
phones on a weekly basis (30% on a monthly basis). The
median number of presently stored incoming messages is
40. Asked for experience in playing mobile phone games
(e.g. Snake or Tetris), the majority of participants stated to
play never (n=22) or to play less than once a month (n=8).
However, nearly every second participant reported to be a
skilled desktop computer game player (n=16).
5 Results
5.1 Methodology
The design comprises two factors (task and design) with
two levels each. The task factor differentiates between the
single contact and the group contact scenarios. The fac-
tor design consists of the graphical user interface and the
list interface. This sums up to four independent variables.
To test for main and interaction effects we calculated one
model for retrieval success, one for the time spent to com-
plete a task and one for the usability questionnaire. The
items of the usability questionnaire were included as dif-
ferent measures in one model.
5.2 Objective results: Time and retrieval
success
The mean completion times for all five scenarios of the ex-
periment are displayed in the column “time” of table 1. Re-
sults show clearly that the fastest way to solve a scenario
was the list interface for both tasks.
Table 1. Objective results (mean values, smaller time spans
and larger percentages represent better results)
Task Scenario & Time Rec. Prec. F1
type interface sec. in % in % in %
Group 2 graphical 115 66 90 75
contact 3 list 98 64 96 76
Single 4 graphical 101 72 90 80
contact 5 list 53 99 98 98
Baseline 6 classical 80 67 91 58
The retrieval success is presented by stating the
recall, precision and F1 values using means. Precision
is defined the ratio of scenario-related messages read
compared to all messages read in the scenario. Recall
represents the relation of messages belonging to the sce-
nario compared to the total amount of relevant messages
found by the participants (eight messages for scenarios
2-5, four messages for the last scenario). Thus, precision
represents a good measure how many false messages
were read. Typically, recall and precision are combined
in the F1 measure, describing the overall performance
(F1 = 2rp/(r+p), r =recall, p =precision). Concern-
ing retrieval success, the main effects for task and design
and the interaction effect were significant (Ftask;1;33= 58.8;
Fdesign;1;33 =28.6; Ftaskdesign;1;33 =16.4; pall =.000). In
addition, all effects concerning time spent to com-
plete a task were significant as well (Ftask;1;33 =20.0;
Fdesign;1;33 =34.5; Ftaskdesign;1;33 =6.5; ptask =.000;
pdesign=.000; ptaskdesign =.016).
Overall, the list interface performed better than the
graphical interface and the single contact scenarios per-
formed better than the group contact scenarios. If we look
at the interaction effects, we see a highly better perfor-
mance with the list interface than with the graphical in-
terface for the single contact scenarios, but only a minor
difference within the group contact.
5.3 Subjective results: Usability question-
naire
Concerning the usability, the interface designs had a signif-
icant effect (Fdesign;5;29=4.3; p=.005) but the tasks had not
(Ftask;5;29=2.4; p=.062). The interaction effect was also
highly significant (Ftaskdesign;5;29 =6.2; p=.001). Figure 3
shows the results and demonstrates the interaction effect.
The graphical design produced significantly better results
with the group contact tasks than with the single contact
tasks. This effect was the other way round for the list de-
sign: single contact tasks were significantly better evalu-
ated than group contact tasks. Similarly to before, the cat-
egorized list design got better scores than the graphical de-
sign and the single contact scenarios were better than the
group contact ones.
Interestingly, an interaction effect exists for the item
Figure 3. Subjective results (mean values, 1 = best,
7 = worst, captions represent the number of the scenario,
the task type and the interface design)
enjoyment. A clear deviation of means for the list interface
is visible in figure 3. Participants enjoyed the graphical in-
terface much more than the list interface to solve the group
contact scenarios, but took more pleasure in using the list
interface over the graphical one while working on single
contact scenarios.
6 Discussion
As for hypothesis H1, both novel interfaces received better
objective and subjective evaluation than the existing clas-
sical interface. Even though the overall time for solving
scenario six with the classical interface was shorter than the
graphical one, it should be mentioned that only four instead
of eight messages had to be found. The same argumenta-
tion applies to the subjective results: The classical baseline
interface might have received even worse results if all eight
messages had to be read.
Hypothesis H2 can be accepted as well. The list in-
terface is superior to the graphical interface, except for the
variable intrinsic motivation. The graphical interface is
more enjoyable. This interaction effect might also be in-
terpreted through the high rate of skilled computer game
players in our sample.
Interestingly, it can be clearly seen from our findings
presented in table 1 and figure 3 that the novel interfaces
differ significantly more for the single contact scenarios
than for the group contact scenarios. As it is reasonable to
state that SMS conversations generally take place in short
time frames, the broader differences for the single contact
scenarios might not be that relevant.
Furthermore, the twofold experimental setup might
have had an influence on how much better a new interface
is in comparison to the classical one. During the planning
phase of the interface design we discussed a combination
of both interfaces where users of the graphical interface
can browse to the preceding or following message from the
same communication partner (similar to the list interface).
We finally decided to use a two-interface study in order to
learn more about the differences between the tasks. Com-
bining the features of both interfaces might still yield an
even better evaluationof the novel interfaces.
Finally, the design of both novel interfaces had to be
slightly simplified. The list interface in its current form ,
for example, would lead to problems with unread text mes-
sages. If two or more unread SMS messages exist in the
message store, users can hardly access them. This could
be solved by allowing users to browse such messages by
pressing the buttons left or right. The graphical interface,
on the other hand, allows for displaying only one message
per hour in its current form. This problem could be solved
by reducing the size of the messages displayed or by apply-
ing zooming techniques.
7 Conclusion
Both novel interfaces used in our experiment yielded better
results than the classical one. Some details of our findings
might have implications for future mobile user interface de-
velopment.
Today’s mobile applications seem to be built around
technologies (e.g. incoming and outgoing text messages
are separated). Novel interfaces could be built around so-
cial contacts. Many participants stated that they especially
liked sorting messages by social contacts. This supports
Tamminen et al., who formulated that applications should
adapt to social contexts of users [11, p. 138]. The graph-
ical interface might benefit from social awareness as well.
The interface could be enhanced by assigning unique icons
to well-known contacts. Depending on display resolutions
this could be everything ranging from small figures to large
photographs.
Commercially, ring tones, sound files and games are a
profitable business. The graphical interface might serve as
a kind of mobile game. It could be played while traveling
or waiting. Moreover, new technical developments might
allow for incorporating SMS messages, e-mails and other
associated documents. Novel interfaces (both textual and
graphical) could facilitate to find the right information at
the right time.
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