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A Study of the Effect of Thumb Sizes on Mobile Phone Texting Satisfaction

Vimala Balakrishnan and Paul, H.P. Yeow

Journal of Usability Studies, Volume 3, Issue 3, May 2008, pp. 118-128

Article Contents


Results indicated that when thumb circumference increased, user's satisfaction towards key size and space between keys decreased. Moreover, users' texting satisfaction was found to decrease when thumb circumferences increased. Mobile phone manufacturers and designers should look into enlarging the keys and increasing the space between keys. This may result in a larger mobile phone and a change in the keypad layout; however, this will be eventually accepted as users' texting speed increases. We also recommend an increase in the number of keys to reduce the key overloading problem. Extended keypads that consist of more keys could be designed and introduced for a more straight-forward way to enter text messages. For example, Nokia E70 comes with a foldable QWERTY keypad. This keypad requires mobile phone users to use both their hands for text entry. The increased number of keys results in a faster and easier text entry. Other mobile phone manufacturers should design similar keypads to be included in their respective mobile phones. Mobile phone users, especially those with larger thumb sizes, will benefit from such designs.

In addition, results also indicated a negative correlation between thumb length and keypad layout. Comments were made about the difficulty of reaching keys that are placed at the right-most column of the keypad. With this knowledge, researchers and mobile phone designers could rearrange some of the keys or letters for a better accessibility. Letters such as T, H, E and N are commonly used in English text. Therefore, these letters can be placed in the middle of the keypad ("sweet spot") for an easier and faster accessibility. Initially it may be difficult to adapt to keypad layout change as users are familiar with the current layouts; however, texting speed can be greatly increased once users get accustomed to the changes. Moreover, an improvement in the keypad layout will decrease the pain felt in the thumbs due to frequently accessing the hard-to-reach keys. Users will be encouraged to message more as they feel more comfortable in accessing the keys and letters, especially the frequently used ones. This recommendation benefits not only those who have long thumbs, but the overall population of mobile phone users as accessibility to the commonly used keys are easier, which increases texting speed and eventually texting satisfaction.


The aim of the study was met as the findings confirm that varying thumb sizes have significant effects on users' texting satisfaction, based on some of the keypad design factors (e.g., keypad layout, key size, and space between keys). With this knowledge, mobile phone manufacturers and designers can create customized mobile phones that suit users with larger thumb sizes by prioritizing key size, space between keys, and keypad layout.

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