Hand Anthropometry and SMS Satisfaction
Paul H. P. Yeow
The effect of hand anthropometry on Short Message Service (SMS)
satisfaction was investigated using structured questionnaire interviews
with 110 subjects, aged between 17-25 years old. Hand size was measured
to assess its effect on mobile phone design factors satisfaction whereas
thumb circumference and length were measured for keypad design factors.
Small hand-sized subjects were found to be more satisfied with mobile
phone dimensions than large hand-sized subjects. Thumb circumference significantly
affects users` satisfaction towards key size and space between keys whereas
thumb length significantly affects keypad layout satisfaction. Both thumb
circumference and length significantly correlate negatively with the corresponding
keypad design factors. Results confirm that hand anthropometry do affect
users messaging satisfaction. These findings should prove useful to mobile
phone designers who could look into the possibility of designing customized
mobile phones that cater to large hand and thumb sized users, so as to
increase their subjective satisfaction.
Short Message Service or popularly known as SMS allows the sending of
short messages (160 characters or few) between mobile phone subscribers.
SMS has been a tremendous success in most of the countries, including
Asian countries like Singapore, Philippines and Malaysia. Malaysians,
for example, were found to have sent 11.7 billion messages in the first
three months of 2007, compared to only 7.4 billion in 2006 (The Star,
2007a). Moreover, a survey among 1,004 mobile phone users revealed that
Malaysians send an average of 17 SMS in a day and spend an average of
RM 101.50 per month to send SMS (The Star, 2007b). SMS is popular as it
is fast, easy and most importantly cheap.
The popularity of SMS has heightened the interest in mobile phone research.
A lot of studies have been done on the adoption of mobile phone and SMS
in certain countries (Faulkner and Culwin, 2005; Ling, 2005; Hõflich
and Rõssler, 2002). Social and psychological effects of SMS messaging
were also studied to examine the underlying motivations of using SMS (Reid
and Reid, 2004). Some researchers have done usability studies of mobile
phones (Soriano et al., 2005; Balakrishnan et al., 2005)
and some have compared the performance of the text entry methods (James
and Reischel, 2001; Friedman et al., 2001). Although numerous studies
have been conducted related to SMS, however very few were related to SMS
users` subjective satisfaction (Yun et al., 2003; Han et al.,
User satisfaction should be the main priority in any product designs.
In Japan, cars, houses and costumes have been designed based on Kansei
engineering, which is a product development technique that takes into
account the desirable features of products as perceived by the end users
(Nagamachi, 2002; Miyazaki et al., 2003; Kashiwagi et al.,
1994). Overall satisfaction was also used as one of the usability factors
to evaluate the look-and-feel of mobile phone designs (Yun et al.,
2003). One can conclude that the success or failure of any product is
heavily dependent on the end users` satisfaction. Literature reviews revealed
no studies investigated the effect of hand anthropometry (physical measurements
of the hand) on SMS users` satisfaction. Some users with large fingers
have commented about the difficulty of using mobile phones to SMS (Axup
et al., 2005; Faulkner and Culwin, 2005) and many have reported
about the shrinking size of the mobile phones (Ergonomics Today, 2005;
Anderson, 2005). These suggest that varying hand and finger sizes might
affect users` satisfaction in using mobile phones to SMS, thus this study
aims to investigate if hand anthropometry affects users` SMS satisfaction,
focusing on mobile phone and keypad design factors.
MATERIALS AND METHODS
Text entry on mobile phones: The standard keypad layout on many
mobile phones consists between 12-15 keys that are overloaded (Fig. 1).
These keys are used to enter text, symbols, numbers and punctuation. Each
key is mapped to between three to four characters, resulting in the users
having to make repetitive key presses for text input. The most popular
forms of text input on a standard 12-key mobile phone are either multitap
or predictive text entry.
Multitap: Successive key presses are made on different or the
same keys to determine the intended letters. For example, to enter SMS,
the user would press 7777 (to get the fourth letter on key-7), then 6
and finally 7777. The break between two letters entered with the same
key is normally indicated by a pause (1-2 sec). Multitap is simple and
unambiguous; however it can be slow (Mackenzie, 2002).
Predictive text entry: With predictive text entry, the mobile
phone displays the most likely word for the sequence of keys pressed since
the last space character. If the predicted word is incorrect, the user
will have to scroll through the alternative words. However, if the word
is not recognized at all, then the user must delete their input and enter
the word via multitap. This can be quite frustrating. Moreover, it is
also impossible to enter numerals, acronyms or any combinations of letters
and numerals (e.g., l8r for later). Users also have to visually monitor
the display to resolve ambiguities, unlike multitap that can be operated
eyes free by experts (Mackenzie et al., 2001).
Design of study: Figure 2 shows the theoretical
framework used in this study. SMS satisfaction acts as the dependent variable
whereas mobile phone and keypad design factors are the independent variables,
tested against hand anthropometry.
Both the independent variables were chosen as they represent the physical
aspects of a mobile phone that directly relate to hand anthropometry.
A mobile phone is held in one or two hands and messages are entered via
the keypads using one or two thumbs. Moreover, a lot of work has identified
these two factors as some of the usability issues of mobile phones (Axup
et al., 2005; Soriano et al., 2005; Balakrishnan et al.,
2005). Table 1 and 2 show the different
factors tested for the independent variables.
All the design factors for mobile phone and keypad were identified from
studies conducted to determine some of the critical mobile phone design
features to users` satisfaction (Ling et al., 2007; Han et al.,
2004; Yun et al., 2003).
||Standard ISO 12-key keypad design
||Mobile phone design factors
||Keypad design factors
Other studies that have reported on issues related to some of these features
are: problems related to tiny keys (Soriano et al., 2005; Kurniawan
et al., 2006),problems related to key size and space between keys
(Balakrishnan et al., 2005; Ornella and Stephanie, 2006) and issues
on the shrinking size of mobile phones (Anderson, 2005; Croasmun, 2002).
None of these studies, however, took hand anthropometry into consideration.
Subjects: One hundred and ten youth ranging between 17-25 years
old were interviewed (mean = 21.5 years, SD = 1.64). The majority of them
(84/110) were recruited from a local university and the rest were selected
from public places (mall, public library etc.). All the subjects had some
experience in using SMS, with an average of 3.8 years and SD = 1.19. All
the subjects also used their thumbs to compose messages. 80.9% (89/110)
of the subjects used multitap for text entry, 11.8% (13/110) used both
multitap and predictive text entry interchangeably and only 7.3% (8/110)
used predictive text entry. The mobile phones used in this study were
by some of the popular brands, namely Nokia with 66.4% of the subjects
owning this phone. This was followed by Samsung (12.7%), Motorola (9.1%),
Sony Erickson (8.2%), Siemens (1.8%) and Alcatel (1.8%).
Hand anthropometry: Different hand anthropometries were measured
for mobile phone and keypad design factors. Users with small hands might
find it difficult to hold large mobile phones and users with large hands
might find it difficult to hold small mobile phones, thus hand breadth
was measured to test if it affects users` satisfaction towards mobile
phone design factors. Hand breadth was measured at the distal ends of
the metacarpal bones (the joints of index finger to the little finger)
with the hand held straight and flat (Fig. 3a). Thumb length might affect
users` reachability of the keys whereas users with large thumbs might
find it cumbersome keying in messages via the tiny keys. Thumb length
was measured from the second joint of the thumb to the tip of the thumb
whereas thumb circumference was measured at the widest point of the thumb
(Fig. 3b). These measurements were taken based on the physical definitions
used by Vasu and Mital (2000). Measurement tapes were used and all the
readings were taken twice to obtain the average measurements.
Questionnaire: An interview questionnaire was developed in English
with two major sections: Section A to obtain the demographic profile of
the subjects (gender, hand measurements, hand used to text etc.) whereas
Section B is for the subjects to rate their satisfaction/dissatisfaction
levels to statements using Likert`s five-point scale, whereby 1 means
Strongly dissatisfied, 2 means Dissatisfied, 3 means Neutral, 4 means
Satisfied and 5 means Strongly Satisfied.
Interviews: Face-to-face interviews were conducted using the above
questionnaire on a one-to-one basis, beginning with the subjects filling
in their background information, which includes their age, gender, finger(s)
used in composing SMS and so forth. The interviewer then measured the
hand and thumb sizes, based on the dominant hands. Subjects were encouraged
to give comments, opinions and suggestions.
||Hand breadth measurement
All verbal comments were noted by the interviewer. Each interview session
lasted for about 30 min. Two interviewers participated in these exercise
that took almost eight weeks to complete.
Statistical tests: Statistical Package for the Social Sciences
(SPSS) software was used to test the statistical significant difference(s)
of the variables. Hand-size groups were tested against mobile phone design
factors whereas thumb length and circumference were tested against keypad
design factors. Analysis of variance (ANOVA), analysis of covariance (ANCOVA),
Tukey Post-Hoc analysis and Pearson correlations were used to analyze
the collected data.
The five-point Likert scale structured interview questionnaire has an
acceptable level of internal consistency with a Cronbach`s alpha value
of 0.73. Table 3 shows the summary of hand anthropometry statistics based
on gender. Three hand-size groups (small, medium and large) were defined
based on the hand breadth: for males, <8.8 cm is small, 8.8-9.2 cm
is medium and >9.2 cm is large; for females, <7.3 cm is small, 7.3-7.7
cm is medium and >7.7 cm is large (You et al.,2005). The overall
number of subjects for each hand-size groups is: 28 small, 43 medium and
||Hand anthropometry statistics
|Note: Dominant hand measurements only
||Mobile phone design factors satisfaction, based on hand-size
|*: Significant at p<0.05
||Keypad design factors satisfaction, based on thumb circumference
|*: Significant at p<0.05
shows that hand-size significantly affects users` satisfaction with
respect to mobile phone dimensions. Tukey post-hoc analysis revealed that
small hand-sized subjects are significantly more satisfied than large hand-sized
subjects (p = 0.001).
Table 5 shows that thumb circumference significantly affects users` satisfaction
towards key size and space between keys. A significant correlation was
found between thumb circumference and key size (p = 0.001, r = -0.309)
and with space between keys (p = 0.004, r = -0.272). Thumb length was
found to be significant only for keypad layout, both also significantly
correlated to each other (p = 0.042, r = -0.194).
According to the p-values in Table 4, hand-size significantly affects
users` satisfaction towards mobile phone dimension. Smaller hand-sized
subjects are more satisfied with the mobile phone dimension than large
hand-sized subjects. A good and comfortable grip is necessary to enable
one to compose messages in an efficient manner, however, this is not possible
for users with large hands who have to struggle messaging while holding
the small mobile phones. The users find it awkward pressing the keys while
holding the small and slim mobile phones in their large hands. This statement
is supported by Margaret Head, the President of Ergonomics Society of
Australia who said that mobile phones are more suited to a young child
than a grown adult (Croasmun, 2004). Nine large hand-sized subjects mentioned
that they only use SMS to send very short messages; otherwise they prefer
making calls as they can carry conversations by holding their phones (no
fumbling with fingers and keys required) or by using hands-free gadgets.
Mobile phone dimensions were also found as one the features impacting
overall satisfactions of mobile phone users by Ling et al. (2007);
however, no hand-size measurements were included.
In Table 5, thumb length significantly affects keypad layout satisfaction,
negatively correlating with each other. This could be due to the 4x3 layout
used by the mobile phones in this study and in most of the mobile phones
in the market as well. It was found that subjects with longer thumbs find
it difficult to reach key -3, 6, 9 and #, which are all placed at the
right-most column of the keypad (Fig. 1). Eleven subjects commented that
they have to practically bend their thumbs or readjust the placement of
the phone on their palms in order to press these keys, especially for
key # which is at the bottom corner of the phone. The motion of adjusting
the hand and thumb to accommodate the keypad layout causes dissatisfaction
among these users. When prodded further, four of them stated that continuously
bending their thumb have caused discomfort at the first joint of their
thumb, especially after continuously messaging. Increase in messaging
may contribute to a rise in Repetitive Strain Injury (RSI) in thumbs,
especially among the young users. Bronwyn Clifford, of the Association
of Chartered Physiotherapists in Occupational Health and Ergonomics (ACPOHE)
mentioned that too much messaging can result in pain and swelling of the
tendons at the base of the thumb and wrist as the thumb is good at grasping
but not good for repetitive movement (Cannon, 2005). The majority of the
subjects (64/110) stated that the keys placed in the middle of the keypad
(sweet spot) were the easiest to be accessed and most comfortable as well.
Thumb circumference was found to significantly affect users` satisfaction
towards key size (Table 5). As mobile phones shrink in size, the key size
shrinks as well. This further complicates the problem of messaging among
users with large thumbs. Thumb circumference was also found to significantly
correlate negatively to key size. This confirms that as users` thumb increases
in size, their satisfaction decreases towards key size satisfaction. Large
thumbed users find it difficult to make multiple key presses on the tiny
keys. This is further aggravated by the limited or no space between keys.
These users tend to accidentally hit the wrong keys when entering messages.
Having to correct the errors cause frustrations among these users, hence
decreasing their satisfaction with respect to key size. This finding is
consistent with Soriano et al. (2005) who reported that four out
of five male participants in their study claimed that the size of the
keys became an issue when messaging especially among those with larger
fingers; however, the researchers did not take any finger measurements
in their study. Small key sizes were also reported as one of the mobile
phone usability problems by Axup et al. (2005) and Ornella and
Stephanie (2006); however none took anthropometric details into consideration.
Anderson (2005) reported that any tool that involves a struggle to be
used earns a D or worse for usability. A common criticism is that mobile
phones have become too small causing aim and accuracy to suffer when adult
hands finger child-sized buttons.
Thumb circumference also significantly affects users` satisfaction with
respect to space between keys (Table 5) and both correlating negatively
to each other. Large thumbed users are more dissatisfied with the limited
space between the keys. Miniaturization of the mobile phones also causes
the keys to be placed closely together; hence limiting the space between
the keys. Large thumbed users find messaging a tedious task due to the
close placement of the keys, which is further aggravated by the tiny key
size. Thirty two subjects commented that they tend to hit the neighbouring
keys accidentally while messaging, especially when it is done in a hurry
or while in motion (e.g., walking, talking etc.). It can be a frustrating
task as they have to waste their time correcting the errors instead of
messaging efficiently. Moreover, they also mentioned that they need to
constantly focus on the screen to make sure they have pressed the correct
key; hence eliminating the possibility of ‘eyes-free` input among
the large thumbed users. Frequently having to correct their errors hinders
these users from adopting SMS at times or to use it only when it is deemed
necessary, for example to send simple and short messages, especially single
line messages. This is especially true among the male users, who generally
have larger thumbs than females (Table 3). Ornella and Stephanie (2006)
also found limited spaces between the keys to be a problem among the elderly
mobile phone users (60-80 years old); however no anthropometric measurements
were taken into consideration. Soriano et al. (2005) found that
spacing between the keys became an issue especially for participants with
large fingers, based on their survey among middle aged-users. Moreover,
subjects with larger thumbs tend to be more careful when making key presses
to avoid making unwanted errors and this increases the time spent on composing
a message. Due to this, subjects tend to make phone calls that are faster
instead of making slow key presses to message.
Key size and space between keys seem to be the major obstacles among users
with large thumbs. The problem is further complicated for large hand-sized users
who also have to struggle holding the small mobile phones while sending SMS.
This shows that mobile phone users are not satisfied with the mobile phone and
keypad designs. Interestingly, the dissatisfaction towards key size and space
between keys exists regardless of the text entry method used as both require
users to make key presses via the keypads. Multitap technique is often criticized
for being slow. An experiment using a mobile phone found that experts and novices
reached about 8 words per minute (wpm) with multitap (James and Reischel, 2001).
In 2003, the world`s fastest mobile texter typed 29 wpm using multitap technique,
which is more than six times slower than the Guinness record of 192 wpm for
the desktop QWERTY keyboard (Starner, 2004). Multitap requires users to make
successive key presses to enter characters and numbers. This complicates the
task of messaging as users with large thumbs find it cumbersome to make key
presses on the closely arranged tiny keys. On the other hand, the predictive
text entry requires users to cycle through possible words as they are predicted
by the mobile phone. Apart from having to make key presses, users also have
to visually monitor the screen to select the desired word. Moreover, users still
need to switch to multitap to enter numerals. These text entry problems coupled
with poor design of keypads greatly cause dissatisfaction among mobile phone
users to SMS, especially among users with larger thumbs.
The effect of hand anthropometry on SMS satisfaction was studied based
on hand-size, thumb length and circumference measurements. These measurements
were tested against mobile phone and keypad design factors. The following
results were drawn:
||Smaller hand-sized users are more satisfied with the
mobile phone dimensions than larger hand-sized users, with regards
to holding the mobile phone and messaging at the same time,
||The increase of thumb circumference decreases users` satisfactions
towards key size and space between keys as messaging becomes tedious
due to accidentally hitting the wrong keys,
||The increase of thumb length decreases users` satisfactions towards
keypad layout as accessing some of the keys becomes difficult and
sometimes causes pain in the thumbs,
||All the above problems were reported regardless of the text entry
method used to enter text.
It can be concluded that hand anthropometry definitely affects mobile phone
users` SMS satisfaction. Customized mobile phones have been designed to
suit the elder people (Croasmun, 2005) and also kids (Budnick, 2005) to
improve usability and increase satisfactions. With this in mind, the results
from this study can be used to design customized mobile phones that suit
users with larger hands and thumbs or even enhance the current designs to
increase the satisfaction among all mobile phone users.
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