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Geneve, 28 mai - 7 juin 1991
Question: 28/I
SOURCE: AT&T
TITLE: Performance, Preference, and Usage for Q and Z on
10-Digit Keypads
1. Introduction
Ten-key pads are used world-wide for telephones, Automatic
Teller Banking Machines (ATMs), and Point of Sale terminals
(POSs). Both CCITT and ISO subcommittees are currently
considering standardization of the placement of Latin
letters on 10-key pads. To date, CCITT SGI,
ISO/IEC/JTC1/SC17, and ISO/IEC/JTC1/SC18/WG9 have agreed
that a common international standard should affirm the
placement of the 24 letters as they currently appear on
telephones, ATMs, and POSs. This telephone layout is
illustrated in Figure 1a. However, the letters Q and Z do
not currently appear on telephones, and there has been much
recent discussion of where they should appear on 10-key pads
in an International Standard. The two possibilities that
have received the most consideration to date have been 1)
placement of Q and Z on the 1 key (Q/Z=1) and 2) placement
of Q on the 7 key and Z on the 9 key in alphabetic order.
These assignments are illustrated in Figures 1b and 1c.
This contribution summarizes results of two studies
conducted to determine if there are usage, preference, or
performance differences that would support one of these
arrangements over the other: A laboratory study examined
performance and preference. A national preference and usage
study among active ATM and calling card users collected
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information on PIN usage and on preferences for the two
layouts.
The following summarizes the design of the studies and their
main results.
2. Laboratory_Study
Subjects keyed in letter strings on DTMF telephone keypads
using each of the two mapping schemes. Three keypads were
used in the study, as illustrated in Figures 1a-c. Half of
the subjects used standard phones without Q and Z marked on
the keys. The others used telephones modified to include Q
and Z on the keypad, half the time using the Q/Z=1
arrangement, half the time the Q=7/Z=9 arrangement.
A total of 64 people participated in this study. Each
subject dialed names, 800 "vanity" numbers, and four-letter
passwords. There were 32 strings of each type, and half of
the strings of each type contained the letters Q or Z. The
letter strings to be keyed in were presented one at a time
in large letters on a computer monitor. Presentation of
lists and mapping schemes were appropriately
counterbalanced.
2.1 Results
Both performance and preference data were collected.
Performance was measured by the number of errors subjects
made in keying a letter string and by the amount of time it
took to enter the letters. Preference ratings were collected
after subjects used each mapping scheme, as well as after
the experiment.
Errors An error was recorded whenever the digits dialed did
not exactly correspond to the letter string presented to the
subject. In addition, any time a subject paused longer than
5 seconds between digits, that trial was recorded as an
error.
Table 1 shows the errors for the two mapping schemes for
marked and unmarked phones. The results show no
statistically significant differences in errors made with
the two mapping schemes.1
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Table 1. Number and Percentages of Errors
___________________________________
| Marked Phones| Unmarked Phone|
|______|_________|_______|_________|
| Q/Z=1| Q=7/Z=9| Q/Z=1| Q=7/Z=9|
|______|_________|_______|_________|
| 134| 133 | 156| 130 |
| 17%| 17% | 20%| 17% |
|______|_________|_______|_________|
Keying Time Total keying time was calculated by adding the
times from first to last keypress and the time from stimulus
presentation to first keypress. Only correctly keyed
strings were included in the timing data. Table 2 shows the
mean keying time in seconds for the two QZ mapping schemes
for the marked and unmarked telephones. Users keyed
slightly faster on marked phones with the Q=7/Z=9 mapping,
but on the unmarked phones using the Q/Z=1 mapping. The
differences found here are small (on the order of half a
second or less) compared to the average time it takes to key
in a string (11.7 seconds).
Table 2. Means and SDs for Total Keying Time (in Seconds)
__________________________________________
| Marked Phones | Unmarked Phones|
|_______________________|_________________|
| Q/Z=1 Q=7/Z=9| Q/Z=1 Q=7/Z=9|
|_____|_________________|_________________|
| Mean| 12.0 11.3 | 11.5 12.0 |
| SD | 2.8 2.2 | 1.6 2.7 |
|_____|_________________|_________________|
Preference Ratings At the end of the experiment, subjects
were asked which of the QZ mapping schemes they preferred.
Table 3 shows the number of subjects preferring each
arrangement.
Overall, significantly more of the subjects preferred the
Q=7/Z=9 arrangement (61% vs 39%).2
__________
1. By a chi square test, X squared = 0.88, p = .35.
1. Binomial test, p =.05.
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Table 3. User Preference for QZ Mapping Scheme
___________________________________
| Marked Phones| Unmarked Phone|
|______|_________|_______|_________|
| Q/Z=1| Q=7/Z=9| Q/Z=1| Q=7/Z=9|
|______|_________|_______|_________|
| 12 | 20 | 13 | 19 |
| 38%| 63% | 41%| 59% |
|______|_________|_______|_________|
3. Field_Study
The objectives of this study were to:
o Assess peoples' preferences for the two Q/Z mapping
schemes and the reasons for their preferences.
o Assess the incidence of choosing personal
identification numbers (PINs) based on letters and
numbers, and of mapping assigned numeric PINs to
letters.
o Assess the incidence of dialing letters on telephones
and ATMs as well as awareness of various situations
involving alphabetic entry from 10-key pads.
o Understand how people currently choose PINs.
3.1 Design
Mall intercept interviews were conducted with 400 people in
four national regions. Two hundred interviews were
conducted with ATM cardholders and the same number with
telephone calling card users. To ensure familiarity with
PINs and calling card use, only respondents who reported at
least weekly use of either card were included in the study.
Interview protocols began with basic screening questions.
Respondents were then shown one of two otherwise identical
telephones that differed only in the placement of the
letters Q and Z and asked to dial a small set of names, PINs
and alphabetical telephone numbers using the dialpad. They
then rated the telephone overall and on several specific
dimensions. Similar use and ratings of a telephone with the
other Q/Z placement, and then ratings comparing the two
telephone layouts, followed. One-half of the participants
saw each of the two layouts first. Further questions
assessed card usage, PIN selection, awareness of alphabetic
dialing situations, actual alphabetic dialing usage, and
demographic variables.
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3.2 Results
Preferred Mapping Scheme Overall, respondents preferred the
Q=7/Z=9 letter placement over the QZ=1 placement, by 83% to
17%. This preference for the alphabetical order mapping
scheme was stable across individual ratings for each
telephone; comparative ratings after experience with both
telephone alphabetical layouts; component ratings of the two
layouts for ease of letter entry, speed of dialing letters,
and accuracy of dialing letters; and for simple direct
preference judgments.
Reasons for Preference and Comments Of those respondents who
preferred the alphabetical order layout (N=331), 81%
mentioned basing this preference on something to do with
alphabetical order, particularly that Q and Z are easier to
find when they appear in their logically ordered positions.
Of those who preferred the Q/Z on 1 layout (N=67),
legibility and ease of finding Q and Z with them on the 1
key were the two most common reasons for preference.
Spontaneous comments by respondents on the Q/Z=1 layout
indicated that 25% found it hard to find Q and Z and 18%
couldn't find Q at all.
Incidence of Dialing Letters Awareness and usage of dialing
letters on telephone dials and ATM pads was high for this
sample of respondents. Two-thirds of the sample said they
had ever dialed letters on a telephone, and 62% do so at
least once a month. One-third of the ATM users report ever
entering letters from an ATM 10-key pad. Between one-half
and one-quarter of the respondents were familiar with
alphabetical entry for 800 telephone numbers, bank card
PINs, or calling card PINs.
Incidence of Choosing/Assigning PINs with Letters
Respondents were asked to provide generic information about
their current ATM and/or calling card PINs. Approximately
20% of calling card owners have chosen their own PIN; nearly
64% of ATM card owners have chosen their own PIN. One-third
of the ATM card owners who have chosen their own PINs chose
an alphabetic PIN. This means that about 20% of ATM card
owners chose aphabetical PINs. For calling card owners,
this number is about 6%. Interestingly, approximately 13% of
those who use an assigned numeric PIN use a word or letters
to remember it. Very few people would be affected by either
placement of Q/Z on 10-key pads in terms of the embedded
base of alphabetical PINs. One-percent of the entire sample
of active card users reports having a Q or Z in their PIN.
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4. Summary
The purpose of the studies reported here was to determine if
people's performance in keying in strings of letters and/or
their current usage or preferences provide a basis for
choosing between the Q/Z=1 and Q=7/Z=9 10-digit keypad
letter-mapping arrangements. The performance results
(errors and keying time) did not provide a basis for
choosing one arrangement over the other. Preference
results, however, support the choice of the Q=7/Z=9
arrangement.
Performance measures - errors and keying time - showed only
small differences between the two alternatives.