Layout Matters on Touch Screens

If you often dial wrong numbers on your touch screen phone, it may not be your clumsy thumbs to blame. Researchers have found that the size and location of keys on a touch screen influence how accurately and quickly people select numbers.

The findings come from a study of volunteers using a touch screen on a PDA about the size of an Apple iPhone. The PDA was equipped with a 3.5 inch screen, measuring 5.3 by 7.1 centimetres (2.0 by 2.8 inches). The study compared three sizes of square keys, measuring 4, 7 and 10 millimetres (0.16, 0.28 and 0.40 inches) across.

Results showed that people were slower at pressing the smallest keys. They took about 50% longer to navigate 4 mm keys than 7 or 10 mm keys.

The smaller keys also caused more errors. Testers made three times the number of errors using the 4 mm compared with the 7 mm keys. On the 10 mm keys, the error rate has halved again.

Key location also influenced how often people made mistakes. The greatest accuracy occurred with keys on the screen's left side. That part of the screen was easiest for right-handed people to see. All the screen testers used their right thumb to work the keypad while holding the PDA in their right hand.

Based on their study, researchers came up with recommendations on what makes a good touch screen layout.