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Bailey, R.W. (2001), Annual User Interface Update – 2001.
Bailey, R.W. (1993), Performance vs preference,
Proceedings of the Human Factors and Ergonomics Society 37th Annual Meeting,
282-286.
Silfverberg, M., MacKenzie, I.S. and Korhonen, P. (2000), Predicting
text entry speed on mobile phones, Proceedings of
CHI 2000, 9-13.
Tullis, T.S. (1993), Is user interface design just common sense? Proceedings
of the 5th International Conference on Human-Computer Interaction,
9-14.
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A few years ago, two studies were published that showed clearly how much
trouble designers had when trying to predict human performance in their
systems (Bailey, 1993; Tullis, 1993). More recently, Miika Silfverberg,
Scott MacKenzie and Panu Korhonen at the Nokia Research Center in Finland
conducted an interesting study comparing two devices. They had users enter
text information into cell phones. One group entered the information using
"one-handed thumb input," where subjects held the phone in one
hand and pressed the keys with the thumb of the same hand. The other group
used "two-handed index finger input," where participants held
the phone in their preferred hand and pressed the keys with the index
finger on their other hand.
Which way do you think is fastest? A group of 101 website designers and
usability professionals were asked to indicate which would elicit the
fastest performance (Bailey, 2001). Twenty-three percent voted for the
"thumb input" and 77% thought the "two-handed input"
would be faster. The Nokia study showed that the two-handed approach was
12% faster than one-handed. In this case, over 3 out of 4 participants
guessed correctly.
A second study compared entry speed using the two-handed approach with
the "T9" approach. T9 is produced by Tegic Communications in
Seattle. T9 uses a dictionary to disambiguate the letters when entering
text into a cell phone. For example, to key "t-h-e" users pressed
8-4-3-0 (the 0-key is used as a SPACE). T9 then compares the word possibilities
to its linguistic database to "guess" the intended word. It
shows the most common word as a default, and if users want to select another
word, they press the star key for NEXT.
The same group of website designers and usability professionals were
asked to indicate which would elicit the fastest performance – the
normal (traditional) way of entering letters into a cell phone or the
T9 approach. Fifty-eight percent voted for the "normal" method
and only 42% thought the T9 method would be faster. The Nokia study showed
that T9 was 35% faster than the "normal" method. T9 was amazingly
fast, allowing entry speeds of 33 words-per-minute, compared with only
21 wpm for the "normal" approach. In this case, over half of
the participants missed the essential cues for making the correct judgment.
Having designers guess the best way of achieving optimal user performance
is very difficult. Their design decisions can be improved by ensuring
that designers are familiar with the research literature, and by effectively
using performance-based usability testing.
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